Wims, you can always make up something that would fit what you want it to fit, but that doesn't mean it's really going to be used. Your example, as I stated, is something that is unlikely to be needed because your first load of the script is already showing that mIRC is running. And if you don't want it to show that mIRC is already running, then you can subtract 1 as stated. It just doesn't show any reason to make changes.
Yes, there are things that are added that can be done easily with scripting. HOWEVER, this request, as I've stated before, is FOR a scripting method. If you already have a scripting method that is easy, what is the benefit of adding yet another one? Besides, if you really want an identifier added, it would make more sense considering your example to request a # of times started identifier. That would be used far more often. Not that I think it is needed, but there is more value in that.
RoCk, an identifier would act just like a variable. You'd still need your IF/ELSE. The only difference is unsetting the variable when done.
As argv0 said, there hasn't been a really good example shown that is using on START and on LOAD correctly that doesn't work well because of how the events are designed. You can determine your event easily with a variable if absolutely necessary, though it shouldn't be necessary in the first place if the events are used properly. Instead of hypothetical scenarios, I agree with argv0 that pball should explain (or show code) his situation. It is almost guaranteed that it can be done easily by using the events properly.