You used to see Silver Certificates (they were almost identical to dollars) that promised the bank would exchange them for an equivalent amount of silver. Not anymore, Jack! The law regarding those has changed, too. Of course, if you do find one, it's worth more to a collector than it's face value anyway.
More money facts:
http://www.snopes.com/errata/penny.htm
--Baloo
------------------It is far less important to agree than it is to understand.http://members.tripod.com/~Bob_Baloo/index.htm