If you had pictures of the whole piston, including the underside, then you could tell if they were forged or cast. But not just from looking at the crown. Cast pistons have a lot of detail on the underside, like manufacturers logo, etc, that forged pistons don't have. Of course, you could cast a piston to look like forged piston, then it would a forged forged piston. Forged piston forgery?