Marking enemy wards on minimap

Hi.

Sometimes, you spot an enemy placing a ward on the map and the only way you have to communicate to the rest of your team is typing on chat (aside from voice communication, of course).

It would be great if you could place some kind of mark on the minimap, only visible to the rest of your team at places where you saw an enemy placing a ward. The mark would fade as time passes, and eventually disappear.

This feature would improve team working and cooperation over the games, specially in solo queue games, where you usually don't have voice communication with your team mates.

My concerns with this is that could be used for trolling if, for instance, a limit to the maximum number of marks on the minimap per player is set (let's say, 3).

What do you think?