I had a VMC years ago that had a disc on the drawbar. When the tool clamped, the disc would actuate a limit switch. Once in a while I had to adjust the limit switch bracket to get it in the right spot.
You're right, in a deeper dive into my manuals, I discovered in an ATC motion diagram: "SOL" is a Solenoid and "LS" is a limit switch, YV15 is Spindle tool Clamp/Unclamp Command, SQ14/SQ24 appear to be limit switches that have to do with feedback as to the condition of the spindle tool clamp, and SPO is spindle orientation which sets the tool holder's dogs in the correct orientation for the changer arm to plunk it into place in the magazine. Booze Daily's suggested that the limit switch may need to be adjusted... I'll look into that too.