When I worked at Radio Leeds in the late 90s, there was one listener who got so fed up with the RDS traffic flag being left on that he complained to the Director General. This resulted in a telling-off for the station from on high, and presenters being instructed on no account to leave the TA flag on. I’m not sure if the customised Canford light was as a result of all this.
ILR 'generally' did it the correct way with the 'beddle-ipp' tones tagged onto the top and tail of the travel intro/outro and bed. Most stations also had a dry set of the tones to fire off incase the 'RDS On' failed to go to 'RDS off'.
I spent a morning at Radio WM in the early 90's, and they had a RDS TA On 'light' in the studio back then.
RDS TA was fired on and off manually, and it was this, that was used correctly or abused spectacularly over the years.
Yes, in the enviroment of live radio with various distractions, the presenter or t/o could forget to switch them off after the travel, but it is difficult to ignore a glowing light straight in front of you for much longer than needed. In some cases, curiously long and someone only noticed after a long station announcement about what was coming up in the next quarter of an hour.
Couple of weeks later, I mentioned that one to the t/o of the show I was sitting in on (he is still broadcasting today, so won't mention him) and he just giggled, and said "well, the button wasn't working correctly, was it, if anyone complains."