This would be a very welcome addition to all turreted vehicles by almost everyone who drives them.
In a real tank you have a 3 - 4 man crew working together with communications flowing between them.
In a Simulation you have 1 player moving between 3 or 4 positions, with no communication, and all too often no other way of knowing exactly where that turret is.
Even if it was as simple as a small directional arrow visible from the drivers seat.
So when you were driving you would have some indication of where you'd left the turret.
You'd then be able to adjust to that if you see an enemy, and adjust the tanks position accordingly.
This is one of those little things that would help make up for the lack of real world clues that a tank driver would have. Like weight shift as the barrel of the gun travels left, etc.