Just a quick note about the new Pop-Up History Trail created by the DIY action-group in the city. The temporary signs went up Friday evening in time for Doors Open Lowell, which was blessed with excellent weather yesterday. The Pop-Up History committee worked for about a year on this new downtown feature in the historic district, putting dozens of fun and interesting facts about the Lowell story out there in public. Think of it as a Lowell twist on the red-line tourist trails in Boston and Salem, Mass.