tbh if you know what a standard piston looks like you can tell if its been machined but you wont know the compression ratio just by looking , usually if its got valve cut outs it means its low comp, also measure the head as the pistons may have been machined to compensate for an overskimmed head hence they are not low comp unless you put a standard head on

are you taking the head off just to have a look??

what was the compression meant to be?