I'm not sure why he has to put up a sign. Why can't he just shrug and say, "I don't understand" (and not serve)? No one should be compelled to learn Spanish. But someone who speaks Spanish can be compelled to learn English if we give them incentives (such as, if I can't understand you, I can't give you what you want) instead of creating a firestorm. If Philly comes down on this guy, then it backfired terribly.
I used to work in a delicatessan when I was in high school, and we always had Spanish-speaking workers coming in and ordering sandwiches, but they always did their best to order in English (or at least have it written down). We didn't start talking Spanish but we helped them enough that they could be functional and come back the next time and order in English - which they did.
I tend bar at the local Moose Lodge. We rent out our bingo hall for private parties, we had one Saturday night and the vast majority of guests did not speak English, or refused to.......I solved my problem of answering the inevitiable Habla espanol question, by responding I do not speak spanish - in FRENCH.
I recently met with the chairperson of the committee on special education for my local public school dsitrict. The person is Hispanic, and while I do not doubt her ability to read and write in the English language, her spoken English is incomprensible. After 15 minutes, I finally said, "I have no idea what you are talking about." So she starts explaining again. I stopped her and said, "Let me rephase what I just said: I cannot understand you because of your accent so let's not waste any more of each other's time. Send me a written report and I'll respond in writing."
Because he wants to be a bigger jerk than that. :~)