It was a typical weeknight at the Gold Club in SoMa. The music was pounding at the San Francisco strip club, the drinks were flowing and a procession of dancers was spinning onstage. But a less distracted observer could spot something new: a sandwich board next to the velvet rope at the entrance. It was marketing the long-standing gentleman’s club at 650 Howard St. to a new customer base that the business hoped to attract in the coming week.