The stamp is a symbol which takes possession of the imaginary. 
? Pierre Restany, ?The Artist’s Stamp? in Timbres d?Artistes exhibition catalog, 1993.

Could you mail a letter with these stamps? Authorities issue stamps to show that a fee has been paid. Governments and companies use the shape and imagery of a postage stamp for commercial purposes, to raise revenue, and generate publicity. Artists have appropriated the form of the stamp to subvert their official roles and comment on their significance.