[TimedToasts]

4chan's system is pretty good. You can display your country or you can pick from a 'meme flag' (Pirate, Gadsen, etc)

Make it optional that you don't need to display it but you cannot misrepresent your country.

[hakkoru]

I used to post on a forum that did this, as well as showing the OS and browser you were posting from. Some users would be funny and modified their user agent so that it said they posted from a Wii.