TS
The emergency exit signs on the BA 32x's are "on" for takeoff (can't honestly recall whether they are on for boarding or switched on later) and are noticeable, because they are rather bright with the lights dimmed.
When they are switched off, after lift off, it is also equally noticeable by their absence.
This may be atypical for the industry, but that wouldn't be the first time for BA, e.g. the monitored approach raises its head from time to time in other fora.