It's no secret that Jason Terry likes to accessorize. His look is well known to NBA followers, and the former Dallas Mavericks guard and new free agent signee for the Celtics laughed yesterday when asked about it at the second annual Reebok Basketball Summit at the company's headquarters. "No question, the high socks and the headband," he said. "Can't play without them." Wearing a white headband bearing his nickname, "Jet," the high socks and a pair of multicolored Reeboks that he designed, Terry was not quite ready yet to reveal the new, more permanent addition to his appearance: a tattoo on his inner left biceps of the Celtics logo with the Larry O'Brien trophy on the leprechaun's fingertip. A photographer who wanted to snap a shot of it was told, "It's still healing."