I was intrigued to see workers in front of the Source Theatre on 14th St. NW over the weekend hanging a marquee sign for the opening of David Mamet’s Boston Marriage on Feb. 17. For one thing, the Source Theatre Company has been basically closed for 2 years. For another, I had heard last month at a neighborhood association meeting that the building was likely being sold to the owners of Bedrock Billiards, who plan…