There are also indicator nodes to the upper-left of the center aiming reticule. These will "light" when your weapon is in-range and ready to fire. You will notice that after you fire a weapon that requires a reload or cooldown period, the indicator will dim, then relight.
We don't have indicators in for "under effective range" weapons right now, but as there are really only 3 (LRM, Arrow IV and Long Tom) it was pushed down on the priorities list. Also, everything leaves the barrel/tubes "active" right now and ready to damage a target. This can lead to people trying to nose-down and point blank the missile weapons, something I hope will be resolved in a future update with a minimum distance of travel before arming.