I've been looking at old Ruger revolvers and found this one.  On the left side of the frame just above the trigger guard is stamped ASO-460.  This is clearly not a serial number, especial if you know these old Rugers.  The actual number is always on the butt, and never contains letters.  Ruger stocks, as well as aftermarket stocks have a slot in the bottom to see the number without removing them from the gun--you can see the number on this gun in one of the photos.

It does almost look like someone at some point tried to alter the serial by changing the starting "160-...." to "460," which would "match" the 460 on the frame, but those could just be scratches.

To me it seems pretty obvious that the frame number is an LE property number, the "A" being the name of a county somewhere and the "SO" standing for "Sheriff's Office."  Back in the day, "office" was used much more than "department," especially out west.

Anyway, enough blathering.  I can just see an FFL taking a quick look and putting down the LE property number for the serial number.