I don't think you understood what he said.
He means, when you fire your weapon, a mini ammo bar appears next to the reticule. If you stop shooting, the bar would fade away until you start firing again. If your ammo falls under, say, 20 shots, it would blink red and stay visible until you reload. (I've lost a lot of fights because I didn't know my ammo was low before I went in)
I think something similar should be done with the health bar on the other side of the reticule.