This is, perhaps, a good idea:

http://tinyurl.com/79lz9

I've shamelessly pinched the idea of this post from a post on
uk.railways by Tony Sayer. Here is a link to his original post:

http://groups.google.co.uk/group/uk....dfbb1c2ad2b923

If your mobile was stolen/found by someone particularly vindictive then
I guess it could also cause a bit of trouble, but I don't think that
negates the positive aspect of the concept.