JasonO and D_P_ scripts will work nicely for your purpose, I would create the marker arrow type, size [0.5,0.5] (setMarkerSize) and just after each setMarkerPos I would add a setMarkerDir with the direction of the unit. You might also play with marker color depending on the damage level of the command vehicle, and setMarkerText for any informative info you want all the players to see about the commanding vehicle, for example an alarming text if the commanding vehicle is enganged in combat, or "empty" is there is no crew inside, "low ammo" if it is running out of mags and things like that. Just some ideas ...
Being this MP, remember to exec the script only on the server.