They will probably cover this in their pre-match briefing. I know I ask mine for a discreet hand signal touching the shirt pocket if they think YC and shorts for RC. Extent of the flag agitation helps also. If you are unsure, just check with them before the match how you should do this. It may be they won't want help, although I doubt that.Got my first game on the line coming up. Just wondering how to hint to the referee a yellow or red when on near side and the Lino has flagged it as a foul.