A simple in between solution would be to allow people to 'mark' enemies by pressing a key while pointing looking at that unit. If possible the game could automatically choose the correct mark depending on what was being looked or aimed at, so if looking at infantry it uses the infantry mark, if a tank then tanks, etc.
If you want to add a fog of war element to it since not everyone in real life was a perfect spotter, you could fuzz the location a bit by adding a randomized offset, with the amount of offset being based on the distance between the player marking the map and the object being marked.
On top of that, leave the current system in place for people who want to manually mark based on landmarks, and to leave marking available for mortars, question marks, danger symbols, etc. Maybe add the ability to mark in different colors so that squads and sides can develop their own codes (for example, red for auto marks and green for manual marks)