| Firearm Type | Primary Location | Secondary Location | |--------------|------------------|--------------------| | Revolver | Bottom of the grip frame (butt) | Inside the yoke cut (under cylinder crane) – often an assembly number, not the real serial | | Semi-auto pistol | Front strap (above trigger guard) or heel of grip frame | Slide (rare) or inside frame | | Modern M&P series | Under the dust cover (frame rail) | Slide plate (varies) |