its not racism....they are just being treated as a minority. An outsider.
And in regard to that post I read.
I have experienced far less racism in Japan than in the US. (I am Black)
And what a came across was more a desire for a lack of conflict. So thats why Japanese Only signs come up. When they find out you speak Japanese and you are polite, those signs dont really mean much. I've never been turned away from any place except once at a 2nd hand store. I asked him why and he said he was sorry but he had bad experiences before with people trying to rip him off.
Otherwise my 8 years in Japan were devoid of it. I got more racism from Americans and Europeans living in Japan.