As others have already said, use the DM channel. Anything said anywhere else (for me) was, at best, 50/50 to be read.In two and a half years of GMing I don't think I had an issue with anyone rolling checks or emoting something in a particular fashion. People were only ever ignored due to me missing something rather than using silence as a sign I was peeved at their behaviour. I found epic traps and hellballs to be a more effective sign by far.
Sometimes GMs get flooded with requests, rolls, whatever and sometimes it is really really hard to keep track of it and answer all in time and I have to admit sometimes the GMs might miss something. The larger the group is the harder it is to keep track in general.
Screeching halt..... man I miss the quest server and pause...