One mark past 1.5 inches. Hope Im correct.
That would be 1 and 9/16 which would make it the Frontier model.
Value as of 2006 was $285 in "poor" to $7000 in "as new".
Yours looks to be closer to "poor".
One thought, this info is based on a picture of a very rough looking gun compared to a picture and brief discription in a book. So, I hope I'm correct..
I inherited a Smith and Wesson .38 S&W 5 shot nickel plated revolver with a four inch barrel. It has the following markings:
3. Right side of barrel: REGULATION POLICE
6. Number on frame on butt toward the trigger guard 20359
That would be the serial number. They ran from 1 in 1917 to 54474 in 1940 (book doesn't narrow down any further).
Note the chambering is .38 S&W, not to be confused with the more common .38 Special.