The FS has an enlarged hammer pin head that fits into a slot in the slide. This was done to protect the shooter in the event that if the slide breaks it will be retained on the pistol by the enlarged pin.
Basically arose from fears created when the military tested the original 92 in the M9 program and broke a couple of slides because they used severely over-pressure ammo. Normal factory loads aren't a problem, but once the news gets out, truths or half-truths or even outright falsehoods become fact.
Yes I have seen a slide on a 92 come apart, but that was after the owner documented over 100,000 rounds!!! Wish I had that kind of money for ammo!!!!