You can attempt to pick it from the sprites using 'pick by uid', then do an 'else' afterwards in-case it doesn't get picked. That way you either know it is or isn't in the sprite.
That's the only way I know how to do that sort of test.
Or you could create an array of uids for sprites whenever a sprite is created, and check the array for if the value exists. That second way might be more flexible?