Welcome to the forum.
Jack, Muley Gil, and DWalt* have given you the straight poop.
Probably an Regulation Police. Does it have a rebated back strap as shown:
Since it doesn't have the S&W logo on either side of the frame, it was made between WW I and 1920 when the logos were left off. By its serial #, most likely the 2nd half of 1919.
*I see DWalt also answered while I was typing.