It's a gong. Sort of a Japanese thing, you see. But it's cool, no doubt about it.
On the subject of cool scoreboard stuff, the opening every night gets me going too. They use the Dave Wills' intro, then they have a great video, Gene Honda says on your feet, they use the board to show the starters in groups (outfielders, infielders), the whole thing works for me. Way to go Brooksie!