the current ping/mark system is simple and could be expanded
holding the button would show a menu of diffrent options. here are some suggestions
a lot of soldiers
tank somewhere- should be visually distinctive to the current tank marker as it wouldnt directly mark the location
enemy rally point
MG emplacement/camping MG
the bots should also change their behaviour depending on what you mark
avoid line of sight to tanks, MGs
trying to get close to the rally point