So if radio Ls-rcr is on air then message appears on main title with reminder to tune in. Message appears every five minutes, if radio is offline - message does not appear.
I wouldn't mind it being one of those random "gray" server messages that pop up every once in a while. Although I do think it's more the DJ's responsibility to advertise their radio session.
Djs can advertise themselves, but they usually just end up asking administrators for help anyway. /news doesn't look very official, and none of the other options look official either. It's easier for someone to notice an official server message, and I'm pretty sure players would be happy to see it popping up in the chat (assuming they're not already tuned in).
You could just make it not send you a message if you're already listening to the LSRCR radio.