my eyes, thanks for moving that pic here.
Wiki
"MS-06S Zaku II Commander Type
Design by Kunio Okawara, the MS-06S Zaku II Commander Type (also known as the Zaku II Custom in some sources) looks very similar to the normal Zaku: so much so that the Earth Federation can generally only tell the difference from color schemes most pilots apply to their units and the increased performance of this version.
The S-Type Zaku II features a squad-leader "antenna" that is mounted on the head on the Zaku II, which is used to distinguish squad-leaders or higher ranking pilots from other squad-members or lower ranking pilots. It also featured a more powerful fusion reactor. In turn, the S-Type Zaku II had greater thrust and acceleration. This allowed them to move at speeds 1/3 faster than a normal Zaku II (in the original TV series, it was stated to be 3 times faster, but this was retconned in the movie trilogy to the more reasonable figure). This made it incredibly dangerous in the hands of the ace pilots it was handed out to, such as the "Red Comet" Char Aznable."