You’ve probably noticed the building more these last few months now, because of the new sign in front of it. Situated on the busy Southern Artery, Route 3A, is one of Quincy’s historic buildings known as the Souther Tide Mill. Here on the Town River sits a post-and-beam building that is one of only five tide mills left in the United States. Souther Tide Mill was once the only mill in the country to have retained both a grist mill and saw mill.