Two South End banks were robbed Monday morning, and witnesses at both banks gave police a similar description of the culprit. At 10:30 a.m., a man wearing a black or navy hat, white shirt, and black shorts passed a note demanding money to a teller at Brookline Bank on Clarendon Street, Boston police said. The man did not show a weapon and fled toward Back Bay, police said. It was not immediately clear whether the man got away with any money. About 20 minutes later, a man in his mid-30s with clothing matching the description of the man who robbed the Brookline Bank branch entered the Hingham Institute for Savings on Tremont Street, police said.