This is shirt with a very fine plaid on it. It’s grey, with tiny white plaid. It has two breast pockets with flaps.
In The Werther Project (10x19), Sam wears this shirt to investigate the house in St. Louis that contains the Werther Box. He wears it until they leave St. Louis.
In The British Invasion (12x17), Sam wears this shirt the morning after their drinking night with Mick.
In Good Intentions (13x14), Sam wears this shirt for the entire episode.