I think it’s a ranging machine gun to aid main gun accuracy. A lot of tanks had them, but the Israeli ones tended to be more prominent. Don’t know if they’re used much anymore, except perhaps as a backup.
M1 Abrams with the TUSK and urban warfare systems have .50s over the cannon as well to add to their firepower as the coax mg was deemed too weak to punch into buildings and heavy cover, as well as lightly armored vehicles. Less for aiming, more for blasting!
"I saw this in a cartoon once, but I'm pretty sure I can do it..."