For temporarily marking loaned items I have seen the use of a
sticky tape that is designed to not be permanent.
It may be the type used in drafting / page mock-up designs, etc.
The number is writen on a small piece and then it is applied to
the object. The tape easily peels off. I do not know, however,
where it was purchased. I have resorted to taking "Post Its" and
cutting small sections of the tacky portion and using this. It
works fairly well and is easily removed. I would not recommend
leaving this on an object for a year, but for a few months it
seems to have no adverse affects.
John Handley