A) To quote the rugby referee from last weekend, we're here to referee, not coach - so if a player doesn't know the IDFK signal that's their lookout, not yours.
B) Which brings me on to asking what everybody else does about signalling for IDFK. I only ever raise my arm, I think only in a rare couple of occasions have I also shouted out that its indirect - but should I? Does everybody else also put a shout out for IDFK? There is a coach locally that on pretty much every free kick will shout out "Ref, is that direct or indirect?", to which I always reply "Is my arm up?" and move on.
If it's in an attacking area, where they might attempt a shot or to put it into the box, I'll do the arm and a shout to confirm it's indirect.
I'm not shouting for every offside though, just the arm for those.