PHILADELPHIA — After joining the mob that overran the U.S. Capitol on Jan. 6, 2021, federal prosecutors say Ian MacBride returned home to Southeastern Pennsylvania with a souvenir to remember his role in the historic attack. He gave a filched “Area Closed” sign, complete with stickers identifying it as property of Capitol Police, pride of place hanging over the bar in the basement of his Douglassville home. He shared photos of the keepsake on his various social media accounts and online, alt-right message boards, government lawyers allege. And three years after the riot that caused millions of…