New to me Colt M1917

[82Trooper]

Good evening:
I recently added a Colt .45 acp M 1917 revolver to my collection. I am looking to learn as much as I can about this piece. The serial number decodes to 1918 production. It is marked "US Property" and has the Army # near the lanyard ring on the butt.
1- would this have been blued initially, and has it been refinished? I would imagine that after 100 the dull finish is too intact to be original.
2- Can anyone here help me decode the other markings on the frame?
I am specifically interested in these two...
"S20" or "520" underneath a small logo of some sort.
And the "3" near the trigger guard.
Attachment 98725Attachment 98726Attachment 98727Attachment 98728Attachment 98729

Thanks in advance for any insight you guys can offer.
Mike

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