Very annoying indeed. We can often see who's initiated the transmission, quite frankly they almost all belong to the same airline. Problem is the so called "radio direction finder" we are using is not so accurate (although in reality it works quite well) to be considered as undeniable evidence. A couple of days ago the circus started over the Netherlands/Germany, I called on 121.5 one of the offenders (the one nearest to my transmitter) who, like a child, pretended he wasn't there...
I think I will be reporting them officially in the future, let's see if we get to something...