A Somerville alderwoman is questioning one of the city’s parking regulations, calling it unwelcoming to new residents. Rebekah Gewirtz has called for a review of the city’s “48-hour rule,” which limits residents to leaving a car in the same on-street space for two days. The policy is not spelled out clearly by the city, she said. “That’s very frustrating, that’s very unwelcoming,” she said in a meeting March 28. “. . . We don’t want to be renowned for that.” Alderman Bob Trane said the aldermen had previously studied the policy and found it is one of the least enforced city parking rules. Typically, it is only enforced after snowstorms or if the city receives a complaint from a resident, he said. The policy will be reviewed by the aldermen’s traffic and parking committee.