You can find some beautiful mathematical stamps online. http://jeff560.tripod.com/. This list has four different links to some great stamps.  Here is another link to stamps that honor math and mathematicians. http://www.wfu.edu/~kuz/Stamps/stamppage.htm  This next site has World Mathematical Stamps 2000, and the first one, has a beautiful graphic in red, blue and black.  The next stamp, if you scroll down, is from Spain.  It looks like there are a lot of interesting stamps, available online that honor this subject.  If you read the book by Robin Wilson called “Stamping Through Mathematics”, you will find her interesting views, based on research she did, that suggest that other countries hold mathematicians, and the subject of Math in much higher regard then people in the United States; and this is why it is easier to find a plethora of stamps from everywhere, and not that many from the U.S.A.  Whatever you believe, the links above will give you lots of stamps (art) to appreciate.