This sort of thing happens from time to time in the US, and the usual response here is that the offended people complain to the local government. More often than not, there are public-decency laws that can be cited, and the town mayor/council/whatever can put pressure on the business to take the sign down. If the local government isn't responsive, folks tend to complain to their state congress member, state Senator, on up the line to their US congress member and US Senator. People here also tend to tip off the local television stations, who compete with one another to cover the story of the offensive sign and to see which station can generate the most outrage (which translates to the highest ratings for that station!).

So don't despair quite yet, Lizzie. Just start complaining to the right people! :-)

Best of luck, and have a happy holiday!
Sharon