If you allow other promoters to use "C-1" to promote their shows, without any complaint or resistance from you, then you are not upholding your trademark. The result of this (in the US, at least) is that you lose your rights to your trademark as your name becomes a generic term.

So another promotion could then come in and create a C-1 Europe, a C-1 USA, a C-1 Japan...without even asking your permission. You would no longer own "C-1". You gave up your rights to the "C-1" trademark by not protecting it.

If Coke didn't protect their trademark, then there would be multiple companies producing "Coke" soft drinks today. Coke would just be another word for Cola, and any cola company could call their product Coke.