Probably some type of assy mark.
A Buffalo Nickel stamped on a penny is worth $800.00. A Jefferson Nickel stamped on a ZN penny is worth $70.00. A Jefferson Nickel stamped on a CU penny is worth $60.00.
It would have been worth $400-$1000, depending on the exact marking. Unfortunately, it has been refinished (they were not made in nickel) and it has lost any collectors value. Depending on condition, $100-$150. I am truly sorry-
Factory option.
No
Nickel plated
After market finish and barrel job. Standard Catalog of Smith and Wesson, 3rd ed., Supica and Nahas
50-500 usd
100-1000 USD
Use a magnet. If the gun is nickel plated, a magnet will stick to it.
Nickel Silver
Blue and Nickel
1979