Super booster

BILL Murray — who’s known for popping up in unlikely places— had a musicfilled Fourth of July weekend. Spies saw the “St. Vincent” star at the Stars + Stripes Festival benefitting the Martha’s Vineyard YMCA — checking out indie rock bands Walk the Moon, ASTR and Alex Winston. “Hewas in the VIP area at [ local shop and the fest’s venue] Flatbread Company,” said a spy. “He was super nice and giving one of the bands advice on where to go and what to check out. He didn’t do pictures, though, because he said he was ‘ on vacation.’ ” Murray does frequent the Vineyard — a few summers ago, he cleaned out a local restaurant’s AC unit when it iced over. Sunday, hewas at the Grateful Dead’s final Chicago show.