I've always been bothered that negroes are pictured in degrading ways in signs, but I thought this crossed the line. I mean, I can take an example from your link.
In this construction sign a negro was chosen to do the most menial work. It's just like portraying mexicans as cleaning ladies in movies. Every cleaning lady is some sort of minority. Which is degrading, like we can't hold real jobs. Mexicans clean, and black men shovel coal. It would bother you too if you had to put up with it.