The listing, USA #2521 1991 Make-up rate stamp, mint has ended.
USA stamp issued to pay part of the postage in 1991 when rates were increased from 25c to 29c ("F" rate), allowing people to use up their older 25c stamps by adding this one...
-> This is definitely one of the worst designed stamps that I've seen the USPS come up with. Very utilitarian and probably not that many saved by collectors, thus making it tough to find 24 years later!
Year: 1991
Catalog # 2521
Condition: full gum, mint never hinged, post office fresh
I have several of these stamps, all identical, the scan is representative of what you will receive.
My general terms for stamp-related Listia lots can be found here (please read, it answers a lot of basic questions):
http://listiarules.webs.com/