The Geneva convention does not specifically mention the .50 Caliber Machine Gun.
As a matter of fact, it is quite often used by tankers for anti-personnel on gunnery ranges.
Also, the target sheet for machine guns is silouettes of personnel.
Features: The Browning M2 .50 Caliber Machine Gun, Heavy barrel is an automatic, recoil operated, air-cooled machine gun with adjustable headspace and is crew transportable with limited amounts of ammunition over short distances. By repositioning some of the component parts, ammunition may be fed from either the left or right side. A disintegrating metallic link-belt is used to feed the ammunition into the weapon. This gun has a back plate with spade grips, trigger, and bolt latch release. This gun may be mounted on ground mounts and most vehicles as an anti-personnel and anti-aircraft weapon. The gun is equipped with leaf-type rear sight, flash suppressor and a spare barrel assembly. Associated components are the M63 antiaircraft mount and the M3 tripod mount.
USMC Fact File
Classification. The eight types of ammunition are used for the following purposes.
(1) Ball. For use in marksmanship training, and against personnel and light material targets.
(2) Tracer. To aid in observing fire. Secondary purposes are for incendiary effect and for signalling.
(3) Armor-piercing. For use against armored aircraft and lightly armored vehicles, concrete shelters, and other bullet-resisting targets.
(4) Incendiary. For incendiary effect, especially against aircraft.
(5) Armor-piercing-incendiary. For combined armor-piercing and incendiary effect.
(6) Armor-piercing-incendiary-tracer. For combined armor-piercing and incendiary effect, with the additional tracer feature.
(7) Blank. For simulated fire (contains no bullet).
(8) High-pressure test. For use only in proof firing of weapons and barrels.
(9) Dummy. For training (completely inert).
US Army FM 23-65