I hardly think it's racial discrimination, it's freedom discrimination. Whites get hassled just as much and as often as blacks in this regard. The people putting up those signs are spineless panty-waists who would rather disrespect us (black AND white) than to tell the Brady Bunch and the rosie odonnel types to stick it where the sun don't shine. (That's "doesn't" shine for you English majors out there)
There's racial discrimination aplenty (from both sides) out there but the anti-self defense zones are hardly a manifestation of it.