Sorry, I'm not clear what you're ashamed of? That there are people that would want to wash in the sinks or that they are not allowed to?
I don't think it would be a fair description of all homeless people to say they belong to an underclass.
It doesn't bother you to be a citizen of a country that has allowed so many people to lose their homes that bathing in a public restroom is now a nuisance frequent enough to warrant official signage?