Mohamed joins having last been on the books at league rivals and neighbours Bath City, who he re-joined in October.
The experienced 33-year-old returned to the Romans after spending time with Eastleigh, Kettering Town and, last season, Weston-super-Mare, and had an earlier stint with Wealdstone earlier this campaign.
Mohamed heads back to Twerton Park for a third spell during his career, following playing time at Swindon Town, Forest Green Rovers, Newport County, AFC Wimbledon, Cheltenham Town, Port Vale, Accrington Stanley and others.
Mohamed played twenty-one times for Bristol Rovers in 2014 and netted 4 goals during a half season loan from Port Vale, and also turned out twenty-three times on loan to Northampton Town that same year, also notching 4 goals.