It is pretty uncommon, but definitely not anything that would be considered RARE at all as far as value. It is just a small simple plate used on all of the S-2 Postwar turbines, (thousands made). Doesn't make that 681 worth more than any other VG-EXC condition 681.
If you get a double stamped body on any rolling stock, it is a different story for value, and that is to someone that would want it, and be willing to pay a premium to own it. Just my opinion.
