If I found myself in such a line, I'd simply tell the next cabbie up that I don't want to ride with him because of his sign because it "offends" me, lol!
I don't believe that we raving racist maniac Christian or Jewish folk have the right to do that - probably the City of Minneapolis would be down on us like a ton of bricks for "discrimination." I don't live there, but this is what I have gathered from Freepers who do.
The Muslims are using this PC stupidity to get ahead.