The play side of the disc is the shiny side, the label side is the dull side. Scratches visible on the label side of the disc are always due to label-side damage, but the reverse isn’t always true. Method #1 – Hold the disc 12″ or so from a light source with the play (shiny) side facing you. If you can see through a scratch, that scratch is definitely on the label side. If you can’t see through the scratch, it is probably on the play side. Use Method #2 to be sure. Method #2 – Tilt disc so you are looking at the scratch from an angle. If the scratch has a reflection in the surface of the disc then the scratch is on the play side. If not, the scratch is on the label side.