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