If it's a genuine Colt frame, it will be marked on the right side just above the grip:
Colt's PT.F.A. Mfg Co. Hartford, Conn USA.
On the left side of the frame, on the rear of the trigger guard will be Colt's Verified Proof mark, which looks like a tiny "VP" in a triangle.
There will be a single letter or number stamped on the front side of the trigger guard.
If it isn't so marked, it isn't a real Colt.
If all it has is a serial number, it's an after market frame somebody assembled with Colt parts, but it ISN'T a Colt.
Colt's PT.F.A. Mfg Co. Hartford, Conn USA.
On the left side of the frame, on the rear of the trigger guard will be Colt's Verified Proof mark, which looks like a tiny "VP" in a triangle.
There will be a single letter or number stamped on the front side of the trigger guard.
If it isn't so marked, it isn't a real Colt.
If all it has is a serial number, it's an after market frame somebody assembled with Colt parts, but it ISN'T a Colt.