Soon ICANN will offer the possibility to register your own domain extension, for instance .yourcompany, .yourname. However, if you want to register a country, city or county name, there are certain restrictions.
1) If you want to register a country, city or county name as an extension, you need to have the permission of the governemt of this country, city or county. For instance if you want to register .london as an extension, you need to have the permission of the government of London. You should be able to prove to ICANN that you have the permission of the government, for example with a document in which the government clearly states that they give you the permission for registration.
2) If you want to register a city name which is used by different governments, you should receive permission of every government. For instance if you want to register .hoboken as an extension, you’ll need to have the permission of the government of Hoboken in Antwerp (Belgium) and of the government of Hoboken in New Jersey (USA). You should again be able to prove to ICANN that you have the permissin for registration of every government.
3) A third important matter is that the registration of such an extension will be quite expensive. The registration of such an extension will cost somewhere between €70.000 and 100.000.
You can find more information about the registration of a city, country or county name.