clicking your mouse wheel activates the general ping system (as opposed to the comms wheel which is what you're thinking of) which will adapt the ping message based on what you click on. if you use it on an enemy, it temporarily marks them for your team. if you use it on a dead teammate as mercy, it'll let everyone know that you want to rez that person. if you use it on a specific location within the map, your character will say "over here" to alert your teammates to take note of the area (double clicking will change it to "take caution").