Based on the triangular shape of the lower serif of the "S", the thickness of the descending loop of the "S", and the apparent sized compared to the lettering of Monticello I would say that you do indeed have a Large "S" nickel. My only hesitation is that the coin is well worn and the photographs are taken at an angle which tends to distort the proportions of things. Please see the photos below. The first photo shows the small "s" mintmark used from 1938-1941. The second photo shows the Large "S" mintmark that is unique to the 1941 issue. Please note the triangular shape of the serif as well as the increased size. The last photo shows the Large "S" mintmark used past 1945. There were no regular issue nickels made from 1942-1945 at the San Francisco mint, only war time issues. Small "s" mintmark (1938-1941) Large "S" mintmark 1941 Large "S" mintmark 1946... Having said all that, I have no idea what a circulated example of this variety is worth. Mid range mint state examples are currently running about $100.
Cool thanks Lehigh for the detailed reply. In the condition that mine is in think its worth maybe $5-$10?
