Well, as far as leaving a signature item, I leave a Norwegian 1 Kronen coin. While it is not personalized, there are not too many in circulation here in Texas.
On the other hand, I have placed a couple of themed caches, (Thor's Quest II currently acvtive) in which I placed a limited number of serial numbered talismans. They seem to be very popular with the local geocachers. For example, in Thor's Quest III, Professor Jones' Diary there will be 21 numbered Thor's Hammers. The problem is the time it takes to craft them.
Hiemdahl