Spencer barrel markings

[CaOH]

I have a model 1860 Spencer (#16760). I have two sets of markings on the barrel under the hand guard. The barrel is matching.

The first is "PM". It's located near the barrel band.

The  second is "1" as in the number. It's located between the screw hole and the receiver.

Can anyone give me insight as to what they are?

[Wdcalhoun2]

I have the same situation.
Mine are P R and can't quite make out the other

Inspector initials maybe???

[Wdcalhoun2]

Just a side note.... the "P" is twice the size of the "R" and the number 6 or 9 is stamped by the screw hole

[CaOH]

I'm confident the letters are inspectors initials, but the number 1 is what I'm more curious about. It's even stranger that yours has a different number.