To clarify what Light Infantry is saying, which is indeed the quickest and easiest indicator ....
The serial numbers of Inglis pistols were individually
engraved on them (i.e. not stamped)
after each pistol was fully finished and assembled, in three places - i.e. on right side of the frame, directly above that on the slide, and again directly above that on the barrel (through the ejection port.)
In other words, the frame and slide serial numbers got engraved
through the parkerized finish into the raw steel, and thus appear to be "in the white" on a pistol that hasn't been refinished. If refinished, the new finish will have filled in the digits on the frame and slide serial numbers.
No. 2 (Canadian Pattern) Inglis pistol with original finish -
No. 1 (Chinese Pattern) Inglis pistol which has been re-parkerized -