FRANKFURT — Torsten Emmel may have looked like an innocent florist, a gentle guy with a shaved head and an apron, clipping the stems of fresh freesia. In fact, he was on the verge of breaking the law.

Mr. Emmel’s crime: Setting a placard on the sidewalk outside his shop advertising that he would stay open from 9 a.m. to 4 p.m. It was, after all, Mother’s Day. But a city inspector noticed the sign and warned Mr. Emmel that it was illegal to stay open so long on a Sunday. Close earlier or be fined, the inspector said.