Because Monaco organises circus festivals every year, it has issued a number of circus stamps, worth a look. Here are some thatI found:
From the DDR (East Germany, 1978);
These stamps are from Serbia, 2002; this is the First day Cover I got because I really was reminded of childhood visits to the circus by the colours and design!
The above two are from Sierra Leone, 1999, SG3133/8 and 3139/45;