Rob Petrie's Birth Mark - Comedy writer Rob Petrie (Dick Van Dyke) on episode No.134 "Odd But True" on the sitcom THE DICK VAN DYKE SHOW/CBS/1960-66 had a unique freckle pattern on his back. When the freckles were connected, they formed an image of the Liberty Bell. He got offered $500 to show it. 

Squiggy's Birth Mark - The moronic character Andrew "Squiggy" Squiggman (David L. Lander) on the sitcom LAVERNE AND SHIRLEY/ABC/1976-83 had a red family birthmark blotch shaped like Abraham Lincoln.  TRIVIA NOTE: The Krusty the Klown character on the cartoon series THE SIMPSONS has a cow skull-shaped birth mark (with horns) on his chest right across from his superfluous third nipple.