it is!

my understanding is the the american discrimination against bare feet and the still shockingly common 'no shoes, no shirt, no service' signs, started as a way to more discreetly target black folk after the civil rights act, as they were more likely to be poor enough to not have shoes. barefootedness had already had an association with poverty for quite a while at that time, and thanks to the legacy of slavery, poverty has always had an association with black people in america.

the anti-barefoot crowd gained more steam through the sixties and seventies as a reaction by conservative business owners against the hippie movement.

so basically, the US's negative attitudes against bare feet have their roots in racism and reactionary anti-counterculture sentiments.

here's an article about this history i found, if you wanna read more.

Yeah the signs used to be on like every shop years ago. I see them less now but still do.

This rule is ancient. I never seen such signs in my life - read about them in history books tho