Fight the Power Fear of a Black Planet Public Enemy

Most of my heroes don't appear on no stamps

This lyric explains that the heroes of the rapper in this case are unconventional or not considered worthy enough of commemoration on a US Postal Service stamp.
Chuck D's heros would include people like Malcolm X and Marcus Garvey which do not appear on stamps.
Role models of Chuck D are outside of the accepted normal mainstream culture and therefore would not be depicted on a United States Stamp, also a defaming statment regarding Elvis and John Wayne both unabashed racists.