This episode is the mail art primer.   (re-issue)

Cling vinyl stamps allow the stamps to be used with an acrylic handle for support. 

Three-color stamps

The TAM Rubber Stamp Archive has a collection of prints of rubber stamps mail-artists have used since 1983. 

 Harriet Tubman stamp for the $20 bill

https://occupygeorge.com/

https://indroneswetrust.tumblr.com/participate

https://www.stampstampede.org/

East Asian seals 

Mulready stationery

https://www.jetpens.com/blog/how-to-use-washi-tape/pt/698

https://every-tuesday.com/10-hand-lettering-enhancements/