Try turning it over
Not a stamp; postal stationery or cut squares.
If you have a Scott Catalogue, try the Back of Book with a
"U" prefix.
Of course, you could search here on SCF for "cut square" and find a couple pages of threads like these:
https://goscf.com/t/35438https://goscf.com/t/32092Have Fun!
KirkS
Posted 01/07/2015 10:04 am
