Finally...
Walbut:
"As a follow on, the T Mk 2 and later Hawks has a 'PINS' caption on the CWP. If I remember rightly it illuminates if the pins are left in with the canopy closed. It was introduced to try and prevent one of the other hazards associated with seats, leaving the safety pins fitted during flight."
I recall this being discussed in the early '90's and originated from a test pilot, familiar to many here, who made the dreadful discovery that he'd flown a sortie with the pins still in (though he wanted it linked to the engine turning). He had gone on about this until he retired and just couldn't get anyone to implement the idea. I've often thought that there is a general ethos in aviation to leave stuff alone for some unfathomable reason and it is a real struggle to get any innovation or improvement made until an accident or incident forces action.
Perhaps an improvement or a correction is seen as an admission that it wasn't perfect in the first place. In the real word nothing ever is.