2. Add 3 keys. F2 - Attack, F3 - Defend, F4 - Attention, this keys opens team chat and you must add coordinates. Small icon will appear on the map. Default coordinates are were you are staying. Time limit, maybe 1 minute, against spam.
If icon are outside of map, show direction like this:

3. Icons direction on top of screen, like skyrim or oblivion. For example, you spawning randomly, you must to defend the base, but for the first time it's hard to understand from where opposite soliders are attacking.