That of course assumes every other script is going to be happy to work on that princible, and while /DEBUG isnt an overly common command i would ever expect to find in a script, it would only take one /!DEBUG command to shut down the identifier alias thats enabling the signals, same for the suggestion of having debug itself trip a signal, it only takes another debug command to no longer be tripping the signal.
The reply arguement of course can be said, dont lets scripts in that do things unless you know what there doing and agree to that, and for this i doubt it would be overly hard to locate the problem script replacing/disabling debug and fix it. And of course there really is only so much that one would really need do in a debug alias anyway, log the debug, adjust mirc settings, ignore an unliked ctcp or dcc (such as the old crash ya with to bigger filename bug a version had).
Personally Im not unhappy with how it is, but i wouldnt be unhappy if the suggested method was offered as well.