Colnago Serial Number.
 

My Colnago has a Campy SR RD with Pat. 83 so I assume it is either an 83 or 84. The frame has "USA" stamped on the non drive side rear drop out and "53" stamped on the drive side rear dropout. Is this the SN?

Nope. It likely doesn't have a serial number. Colnago, like a number of Italian makes, didn't use SN's until after your frame was made.

Any ideas what the "USA" and "53" indicate and who may have stamped them?

I can't say about the "USA." The "53" is typical on Colnagos on the driveside dropout, but there's no rhyme or reason anyone's been able to decipher. Maybe some kind of code, or some way to match the frame to the fork. I'll ask Ernesto next time I see him.

USA on the non drive side indicates a frame not ready for the domestic market, but good enough for those Americans.

Seriously, ask Colnago, they have been setting up Colnago USA to take control of the Brand here in the USA.

Well it is "Colnago America" and they do not have an active web site.

Next time I have lunch with Ernesto, I'll ask him why he sends rejects to the states! This one was because the Campy SR HS crown race broke on installation due to the overspray on the fork. Too big a diameter, splitting the CR.