An especially loud whistle before a throw-in is also a useful mechanic, I've found, when in small gyms with yappy parents sitting on the sidelines.
BTW, before FC throw-ins, I always say "IN" - and use a short whistle after delays of any kind.
I seem to recall some disagreement on another thread a while back on whether to tell a player they "have the whole baseline" or not. I usually do - something short, like "WHOLE BASELINE" or "ON THE SPOT".