Uncle Tom. Calling someone a Handkerchief Head is synonymous with someone calling a person an Uncle Tom, referencing the book 'Uncle Tom's Cabin.'
The meaning of these two slang names is that they are referring to a black person that collaborates with white people to fit into the mainstream white culture, seeming subservient to white culture without fighting for the rights of black people.
Both of these slang names are meant to be insulting. In essence, it's similar to Malcolm X's complaints of the older generations of black people not fighting hard enough for their rights.