1972 McGovern button what does symbol represent above name

[captainsimosreturns]

This is a 1972 McGovern button when he ran for president. Does anyone know what the symbol represents above his name. Looks like a hamburger bun? 

[wastingtime101]

Theta shaped ecology symbol. The symbol is a combination of the letters O and E from the words environment and organism.

[captainsimosreturns]

Thank you very much for the information.