well it can be both - it could be registered in the USA say - but that does not mean that registration is legally in force world wide [the world being what it is], however it may still be a trade mark, but unregistered, in some of those places

websites have to look at the global picture

whats the difference between registered and unregistered?... heres some initial reading:
http://en.wikipedia.org/wiki/Trademark

I see Bill has answered - getting a registration in every corner of the globe can be time consuming and difficult, even for the proverbial multinationals.... especially if there is dispute with someone