Here's a blurb about that I found:
During the Fourth Series, a model known as the "Bobbed Detective Special" with double action only lockwork and a de-spurred ("bobbed") hammer was offered.
So if yours is a double-action only, it may be an original bobbed-hammer version. If it's double/single-action, then the hammer might have been modded after the fact.
I bought a brand new Smith Model 60 for my wife a while back but her only complaint was that the hammer would snag on stuff in her purse.
Then one night, she accidently dropped it on a concrete floor and the tip of the hammer broke off, so I just "Dremeled" the sharp remaining knub to be rounded over and nice and smooth.
With her newfound bobbed-hammer "version" of her Model 60, she got to like it a lot. I liked it too and keep thinking I should do the same to my own Model 60.