MARBLEHEAD – Police are looking for the person who used a handgun Saturday to rob the Beach Bluff Cleaners on Humphrey Street.Shortly after 10 a.m., a man described as being in his 20s demanded money from the store clerk. Police said he lifted up his shirt and showed the victim a black handgun sticking out of his pants pocket. The gun was not brandished, police said.The suspect fled on foot on Humphrey Street toward Swampscott, but it was unknown if he got into a vehicle, according to police.The suspect was described as about 5-foot-7, weighing 170 pounds with blue eyes and light brown eyebrows. At the time of the robbery he was wearing blue jeans, a blue hooded sweatshirt and a lavender turtleneck pulled over his nose.Anyone with information about the robbery is urged to contact Detective Sean Brady of the Marblehead police department at 781-631-1212.- Dan O’Brien