My guess would be it's not factory. I've never seen any front sights marked "Watson" on early 39a's. Most were either unmarked, or were Lyman or Marbles optional sights.
Marlin lever actions 1870's-WWI, Ballards, and single shot rifles!
I could be wrong, but the C prefix guns were the first 39A's to have factory hooded front sights I believe. The pre-war B prefix guns never had factory ramped/hooded sights I don't believe. At least that is what I have seen.