The Commercial Overprint Society of Great Britain (COSGB) was an online association of people who share an interest in commercial overprints. Commercial overprints (or as they are sometimes called, security overprints) are postage or revenue stamps that have been commercially printed with the name of the user prior to being used.

In Great Britain, Ireland, and New Zealand, these stamps were used to pay an excise tax and were applied to receipts of various sorts. They were generally not supposed to be used for postage, but there are exceptions to this rule. The first overprint user, the Oxford Union Society, used overprints exclusively for postage. And after the end of the excise tax in 1971, firms used their remaining overprints as postage. Other countries used commercial overprints differently: in Canada, New South Wales, and Victoria, these overprints appear only on revenue stamps; in Ceylon, Hong Kong, and Japan they appear only on postage stamps and were used only for postage.

Our main initiative is an online blog that presents topics in the field of commercial overprints. Your comments and criticisms are welcome—you may even submit an article, if you like. These are the articles that have been written as of 13 August 2011:

Articles on Companies
Aberdare Urban District Council
Aldgate House, London E.1 (Portals Limited)
Anchor Line (Henderson Brothers) Ltd.
George Angus & Co. Limited
Arnott & Co. Dublin Limited.
Arthur and Company, Limited
Arthur and Company, Limited, Part 2
Herbert Ashman & Co.
Associated Newspapers Limited
Australian Mutual Provident Society
The Automobile Association
Ayrton, Saunders & Co. Ltd.
B. & H. G. G. Co.
BUPA
Bainbridge & Co. Limited
Bank of British West Africa
Henry Bannerman & Sons Limited
Barings Bank
John Barker & Co. Ltd.
Samuel Barrow & Brothers
Baxendale & Co. Limited
Benetfink & Co.
J. W. Benson Limited
Bentalls
Bevington & Sons
Barry, Ostlere and Shepherd
City of Birmingham Gas
Bon Marché
Bourne and Hollingsworth
Frederick Braby & Co. Ltd.
Bradbury & Co.
Bradbury Greatorex & Co. Ltd.
Bradford Corporation
George Brettle & Co. Ltd.
Brighton & Hove General Gas Company
Bristol Water Co.
Britannic Assurance Company Ltd.
The British Drug House Ltd.
"British Engine"
British Linen Bank
British Oxygen Company Ltd.
Jonas Brook & Brothers
H. H. & S. Budgett & Co. Limited
Bulloch, Lade & Co., Ltd.
Burberry Limited
W. J. Bush & Co. Ltd.
C. & M. Stn.
J. W. Campbell & Co.
Canadian Pacific Railway Company
Capper Son & Co.
Carreras Limited
Carters Tested Seeds Limited
Catesbys Limited
Sir Joseph Causton & Sons Limited
Cerebos Ltd.
Charrington Gardner Lockett (London) Ltd.
Charringtons Gardner Locket (London) Ltd.
Children's Society / Waifs & Strays
The Clay Cross Company
Cluttons
Cohen & Wilks Ltd.
Colonial Bank
Colthurst & Harding
Comptoir d'Escompte de Paris
Cook, Son & Co.
Copestake & Co.
County Perfumery Company Ltd.
Courage & Co.
M. A. Craven & Son
Credito Italiano
Crosse & Blackwell
Crowden & Garrod
Croydon Commercial Gas and Coke Company
Donald Currie and Company
Cussons Sons & Co. Ltd.
Daniell & Sons Breweries Ltd.
Dawbarn & Sons
Day & Sons Crewe, Limited
Thomas De La Rue & Company Ltd.
Debenham & Freebody
Dent, Allcroft & Co.
Derry and Toms
Devas, Routledge & Co., Limited
Dickins & Jones
John Dickinson Stationery
John Dickinson & Co. Ltd.
James Dilworth & Son
Direct United States Cable Company
Dolgellau R.D.C.
Dollond & Aitchison
Dottridge Bros. Limited
Dresdner Bank
Dugdale Bros. & Co.
Dunns Farm Seeds Ltd.
East and West India Dock Company
East London Water Works Company
East Surrey Water Company
Edinburgh & Leith Corporations Gas Commissioners
Ediswan
Elder Dempster & Co. Ltd.
The Ellerman Lines Ltd.
Max Emanuel & Company
Evans Sons, Lescher and Webb
D. H. Evans
Express Dairy Co. Ltd.
Frederick Finn & Sons Limited
Flower and Sons Ltd.
The Fore Street Warehouse Company Ltd.
Foster & Braithwaite
Fremlins Ltd.
J. S. Fry & Sons
A. W. Gamage Ltd.
The Gas Light and Coke Company
Gellatly, Hankey, Sewell & Co.
General Electric Company Limited
W. & A. Gilbey Ltd.
Glyn & Co.
Frederick Gorringe
J. H. Gosling
Great Southern and Western Railway (GS&WR)
Great Western Railway
W. Greenwell & Co. (W. G. & Co.)
J. & A. D. Grimond
D. Gurteen & Sons Ltd.
Guardian Assurance
Hammond, Turner & Bate
Hancocks & Company
Samuel Hanson & Son Limited
Harrods
Harvey, Nichols and Co.
Heal & Sons
Heelas
G. Hitchcock & Co.
Hong Kong & Shanghai Banking Corporation
Hongkong and Shanghai Banking Corporation
W. H. & F. J. Horniman & Co. Ltd.
R. Hovenden & Sons Ltd.
Thomas Hubbuck & Son /a>
Hull
M. Huntbach & Co. Ltd.
Illustrated London News
Imperial Ottoman Bank
Indo-European Telegraph Company
Insurance Industry in India
Jones & Higgins Ltd.
Jones Sewing Machine Co. Ltd.
James Keiller & Son Limited
N. Kilvert & Sons Ltd.
Kodak S. A.
S. Lendon & Sons
Frederick Leyland and Co. Limited
Lewis's
Lima Light Power & Tramways Company
Liverpool Gas Company
Lloyd, Attree & Smith
Lloyds Bank
Logomia
Joseph Lucas Limited
J. Lyons & Co.
Manufacturers Life
Maple & Co. Ltd.
Mappin & Webb
Marshall & Snelgrove
S. Maw, Son & Sons Ltd.
McVitie & Price, Ltd. / United Biscuits Ltd.
Metropolitan Water Board (M. W. B.)
Michelin Tyre Co. Ltd.
Miller and Sons Limited
H. Millward & Sons
Samuel Montagu & Company
Morgan Crucible Co. Ltd.
I. & R. Morley
The Morning Post
C. & E. Morton Ltd.
Mullens, Marshall & Co.
R. S. Murray & Company Limited
N. E. R.
National Bank of New Zealand
National Westminster Bank
News of The World
Newspaper Companies
H. J. Nicoll & Co.
North Central Finance Ltd.
Norwich & London Accident Insurance Association
John Oakey & Sons Ltd.
Old Betty Plant's Ltd.
Oriental Bank Corporation
Orme, Evans & Co. Ltd.
Overseers of Bristol/Overseers of the Poor
Oxford Union Society
P. B. & W. Ld.
Parker, Winder & Achurch Ltd.
Alfred B. Pearce & Company
Pearl Assurance Company Ltd.
Peek Brothers & Co.
Peek Brothers & Winch Ltd.
Peek Frean & Co. Limited
Pellatt & Co.
Peninsular and Oriental Steam Navigation Company
Petty, Wood & Co. Ltd.
Pfeil & Stedall
J. & N. Philips & Co. Ltd.
Pickfords
Edward & Thomas Pink
Pontings
Poplar Borough Council
Portals Limited (Aldgate House, London E.1)
John Pound & Co.
H. D. Rawlings
Read Holliday & Sons Ltd.
Russian Bank for Foreign Trade
Jeremiah Rotherham & Company Ltd. (J. R. & Co. Ltd.)
Rownson, Drew & Clydesdale Ltd.
Rowntree & Co. Ltd.
Peter Robinson
Rylands & Sons Ltd.
Samuel Brothers Limited
Schweppes Ltd.
Scottish National Insurance Company
Selfridges & Co.
Seymour, Pierce, and Chalk
Shell-Mex and B.P. Ltd.
Silber & Fleming
Smiths English Clocks Ltd.
Smith, Payne & Smiths Bank
W. H. Smith & Son
Smiths, Gore and Co.
Henry Sotheran & Co.
Spencer, Turner, & Boldero
Spirella Corset Company
Spottiswoode & Sons
Stapley & Smith Limited
Stewart & McDonald Limited
Stoke-on-Trent
Surridge Dawson (Holdings) Ltd.
Symbol Biscuits Limited
T. Tapling & Co. Ld.
T. Tapling & Co. Ld. part 2
Taylor Brothers Limited
J. R. Tennent
Thornton-Varley Ltd.
The Times
Tod Brothers & Co.
A. & R. Tod, Ltd.
Tottenham & District Gas Co.
Trapnell and Gane Ltd.
R. Twining and Company Ltd.
Union Bank of Australia Ltd.
Union of London & Smiths Bank Ltd.
Vacuum Oil Co. Ltd.
J. Veitch & Sons
Vick, Ashworth & Co.
Vyse, Sons and Company
Waifs & Strays / Children's Society
John Walsh Ltd.
Walton-le-Dale
Waters & Son
Waterlow & Sons Limited
Watson & Philip Ltd.
Angus Watson and Co. Limited
S. & J. Watts & Co.
Waukenphast Ltd.
Webb & Sons
Welch, Margetson & Co.
Richard Wheen & Sons
William Whiteley Limited
Wiggins, Teape & Alex. Pirie Ltd.
W. D. & H. O. Wills Ltd.
Woodhams & Levy
Woolland Bros. Ltd.
Miscellaneous Articles
6d. and 1s. Commercial Overprints
A Catalogue of British Commercial Overprints
Collecting the George V Issues of 1912
Displaying Commercial Overprints
Great Britain—Receipt Duty
Map of Local Government Overprints on SG 518
Overprints and Local Government in Great Britain
Perfinned Commercial Overprints
Printing Errors on Commercial Overprints
The Sloper Records
Receipts
The Sloper Records
Underprinted Advertisements