The lens max aperture signal post is like a block on the 6 o'clock position. It is part of the AI spec. The -S specification adds the lens focal length notch at the 9 o'clock position and a linearity to aperture range.
The only Nikon that was made to take full advantage of an AIS lens is the FA. The FG, F301 and possibly the F501 use some elements to provide the Program mode. Only the FA is capable of Shutter priority and Matrix metering with those lenses.
The F4 uses the max aperture signal post to allow Matrix metering with AI lenses.