By unanimous vote, the San Diego City Council approved an ordinance Monday forbidding the posting of political signs in the public right-of-way. The council postponed setting penalties for such a practice, however, until the city attorney could draft language making the offense a civil violation and not a misdemeanor. The council did so after Mayor Roger Hedgecock expressed concern about criminal penalties, noting that they could be used against unpopular candidates. The new ordinance repeals a previous ordinance exempting political signs from the citywide sign regulations. That exemption was approved in July, 1983, after a sign firm, Candidates Outdoor Graphics Service, sued the city over the restrictions on political signs and was granted a preliminary injunction. After the sign firm dropped its suit, City Atty. John Witt proposed reinstating the regulation, and the council voted to do so Monday.