I tried something similar to this, but had the marker initially set to invisible.
In a multiplayer mission, I had a trigger that, when it detected resistance, would set the marker type to "dot" (Can't remember the specific type).
However, it only appeared to work for the one player. I thought that triggers were client side and that it would have changed that marker for each client - when that client had detected the resistance which would set the (repeating) trigger? There wasn't any desync issues, so is there something that I was missing with trying to do that?
(Or should I just set it up server side?)
Cheers,
Axek.