I was wondering too....
Found this on wikipedia:
92S
In order to meet requirements of some law enforcement agencies, Beretta modified the Beretta 92 by adding a slide-mounted combined safety and decocking lever, replacing the frame mounted manual thumb safety. This resulted in the 92S which was adopted by several Italian law enforcement and military units. The later relocation of the magazine release button means these models (92 & 92S) cannot necessarily use later magazines, unless they have notches in both areas.
[edit] 92SB (92S-1)
The extremely rare 92SB, Initially called the 92S-1, was specifically designed for the USAF (US Air Force) trials (which it won), the model name officially adopted was the 92SB. It included the changes of the 92S, added a firing pin block (thus the addition of the "B" to the name), and relocated the magazine release catch from the bottom of the grip to the lower bottom of the trigger guard.
* 92SB Compact (1981 – 1991), shortened barrel and slide (13-round magazine capacity). It was replaced by the "92 Compact L"..
[edit] 92F (92SB-F)
Beretta modified the model 92SB slightly to create the 92SB-F (the "F" added to denote entry of the model in U.S. Government federal testing) and, later, the 92G for French Government testing, by making the following changes:
* Design of all the parts to make them 100% interchangeable to simplify maintenance for large government organizations.
* Modified the front of the trigger guard so that one could use finger support for easier aiming.
* Recurved the forward base of the grip to aid aiming.
* Hard chromed the barrel bore to protect it from corrosion and to reduce wear.
* New surface coating on the slide called Bruniton, which allegedly provides better corrosion resistance than the previous plain blued finish.
[edit] 92FS
The FS has an enlarged hammer pin that fits into a groove on the underside of the slide. The main purpose is to stop the slide from flying off the frame to the rear if it cracks. This was in response to reported defective slides during US Military testing.