What is a stamp Scott number?
Scott is a company that publishes a listing or catalog of all of
the issued stamps in the world. They assign each stamp a number. A
normal stamp used for postage on envelopes or cards has a plain
number, such as US #1257 or GB #579. There are letter prefixes used
that help identify other types of stamps, such as a C for airmail
as in US #C47, or J for postage due Belgium #J151.
These numbers allow collectors to know that they are talking
about the same stamp and are often used in auction catalogs and in
files.