Focus Target with a controller?

[Z3M0G]

If you're trying to mark a target for others to attack, you select your target, press the Square button using Dual Shock notation(or X if using a logitech F750 or 360 controller), select 'mark' from the mini menu, select an icon to use, then hit accept on your controller and that's it.

And you can also choose to hotkey the mark command from this menu.