I think the arrow or mark should do well for Q. You know, Q is currently rather unreliable. For these reasons
1. Sometimes you spot something in the middle of the map, outside the base, and it says 'spotted 1 infantry/vehicle near a building', giving the impression that the enemy has already infiltrated the base when they haven't
2. At the very least, it should give out the type of the enemy. (eg. : 'Spotted 1 APC near Power Plant' or 'Spotted 1 Technician near Airstrip') at least that saves us from saying an 'APC inc', or 'Sakura/Havoc in tunnel', which as quick as it might, will still leave us quite vulnerable for a second
At least once you spot something and Q it, you should also give out its' current location, at least for a second or 2, whether in mini map or with diamond rectangle like seen by the guy who Q'ed it. Right now it only indicates the existence, but not really helping with the location of things