If hearts are the symbol for love, what would you say best fits as the symbol of hate?

The Nazis appropriated it from other cultures. Being a fairly simple symbol, it shows up in religions around the world. "Nazis" are not the first thing most Indians think of when they see a swastika.

I agree that in western culture it's pretty synonymous with a host of vile connotations, and it's been successfully appropriated - like red baseball caps. But it's not fair to the swastika, and it certainly isn't a universal meaning for the symbol, whereas the heart has no other meaning for most people in the world; that is, of there's any symbolism assigned to a heart by a person, it's probably "love."

I can't suggest a similar, universal symbol for hatred, although as someone else suggested, a clenched fist is probably a good candidate. 👊🏽