Until the 1960's, most places in the South that DID serve Black people were boycotted by their regular White customers.
The real point of previous rulings is that it is free speech to say you reserve the right to refuse service to anyone, but to actually do so based on race or sex was illegal.
After this was ruled on, the signs slowly vanished. I haven;t seen one since around 1976, in Lumberton, North Carolina.