On a QO breaker, how do I distinguish GFCI from overcurrent trip?
Older Square D breakers
Square D does not provide any means to distinguish type/reason of trip.
Newer Square D breakers (date code 1130 and newer)
These breakers (at this writing) have white or purple TEST buttons.
The &quot;Time Saver&quot; (heh) diagnostics provide a method for the breaker to tell you the cause of the last trip.
Link.... link.
Generally the procedure is to turn the breaker off, hold down TEST, turn the breaker back on continuing to hold down TEST, and time the number of seconds until the breaker trips again.   The amount of delay (if any) reveals the trip cause - ground fault, arc fault, or overcurrent.
Note that Square D arc fault breakers have weak ground fault detection (for the purpose of detecting hot-ground and neutral-ground parallel arc faults) — so they can in fact trip on a ground fault indication.