Editing Overprint (section)

== Security measures ==
Overprints have been used as security measures to deter misuse and theft.<ref>Williams & Williams, p. 253.</ref> In the nineteenth century, Mexico was plagued by thefts of stamps on their way to remote post offices. To address this, stamps were shipped from Mexico City to the local districts where they were [[Postage stamps and postal history of Mexico#District overprints|overprinted with the district name]] – they were not valid for postage without the overprint. 
 
In El Salvador a significant quantity of stamps was stolen from the San Salvador post office in 1874. As a result all remaining stock was officially overprinted 'Contrasello' preventing usage of the non-overprinted stamps.<ref>{{Cite web |url=http://www.seymourfamily.com/ElSalvadorHandbook/ |title=El Salvador Handbook - Chapter 3: 1874 - 'Contrasello' Issue |author=Gallegos, GF |year=2002 |access-date=16 June 2019 |archive-date=16 June 2019 |archive-url=https://web.archive.org/web/20190616074728/http://www.seymourfamily.com/ElSalvadorHandbook/ |url-status=dead }}</ref>

The United States used a similar strategy to deal with thefts in [[Kansas]] and [[Nebraska]] in 1929, overprinting the current [[Definitive stamp|definitive issue]] with "Kans." and "Nebr." before they were shipped from Washington, to make it more difficult to sell stolen stamps outside the indicated state.

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File:Stamp Mexico 1864 1r eagle.jpg|[[Postage stamps and postal history of Mexico|Mexico]], 1856: [[Guanajuato]] district overprint
File:El Salvador 1874 type 3.jpg|[[Postage stamps and postal history of El Salvador|El Salvador]], 1874: Contrasello overprint
File:1891 British Government Parcels stamps.jpg|[[Postage stamps and postal history of Great Britain|Great Britain]]: Victorian stamps of 1891 overprinted for use only on government parcels
File:Stamp US 1929 6c Kansas.jpg|[[Postage stamps and postal history of the United States|United States]], 1929: Kansas state overprint
File:DBPB 1948 19 Freimarke Schwarzaufdruck.jpg|[[Postage stamps and postal history of Germany|Germany]], 1948: Allied control mark for [[Berlin]] postage
</gallery>