it seems to be the housing for an adjustable sight - there are 5906 models both with it and without it
see also the Browning Hi-Power for another pistol with both such variants (and where the adjustable sight one also shows why you might want to have some protective wings for it, although this one's much larger, people tended to be pretty overly optimistic about the distances at which pistols could be effectively fired at early on)
NO BUYING, SELLING OR TRADING of guns or accessories. Take that to Reddit and /r/GunAccessoriesForSale or Armslist.com
Censor all personally identifiable information in posts including serial numbers on firearms.
Any post or comment advocating illegal action will be removed and the poster warned. A second infraction will result in a ban.
Unironically suggesting the SKS as a usable rifle in the 21st Century when there are things like the AK and AR that cost only a bit more might result in a ban, it depends on how we feel.
Discussion of hunting is acceptable but please put "CW: hunting" in post titles. Debating the ethicality of hunting is also fine, but keep it civil and don't derail other people's threads.
it seems to be the housing for an adjustable sight - there are 5906 models both with it and without it
see also the Browning Hi-Power for another pistol with both such variants (and where the adjustable sight one also shows why you might want to have some protective wings for it, although this one's much larger, people tended to be pretty overly optimistic about the distances at which pistols could be effectively fired at early on)
Correct, adjustable sight.