Lets take a look at all the times that motorcycles have been used during war on earth.
In the US, motorcycle testing began as early as 1913. There first deployment was during the "Boarder War" against Pancho Villa. They came in a variety of models including standard bike, sidecar support vehicle, sidecar machine gun nests, and sidecar supply runners. They were deemed so effective that over 100,000 motorcycles were commissioned during WWI.
During WWI Entire infantry units could be motorcycle bourn, and motorcycles could be equipped with features such as stretchers, shielding, passenger sidecars, and machine guns. However, the most common use of motorcycles was information relay. The unreliability of radios and other communications during the time gave a great niché for motorcycles to occupy.
The U.S. wasn't the only one with motorcycles though; the British had 30,000 of their own, complete with a range of accessories such as sidecars, machine guns, and ammo storage. Once again, they saw most use as communication relays.
This is a trend that continued into WWII. Despite over 200,000 motorcycles used between allied forces, they were almost all exclusively non combat. American models were the most durable motorcycle available with a Thompson submachine gun holster equipped to hold the soldiers' weapon.
One unique use of motorcycle was as an accessory to paratroopers. Light weight versions of motorcycles were used during WWII by British forces to deploy highly mobile units behind enemy lines. Unfortunately for mars, the lack of atmosphere makes this innovation impossible.
With the conclusion of WWII, many advanced technologies began to be developed, which almost entirely closed the need for on ground communications. This relegated motorcycles to mostly recon work, especially during Operation Desert Storm, in which they got a fair amount of use by Britain, the U.S., and NATO.
Today, the U.S. Military still has motorcycles in reserve. These bad boys are silent electric bikes with 3500 hours charge and 50 hp. I imagine you'll probably have something similar on mars, do to the lack of fossil fuels.
And what uses would they have? Well, if mars has yet to build a good communications infrastructure you may need to use them in part for communication relays.
There's also the possibility that trenches aren't feasible on the rocky surface of mars. This gives mobile machine gun nests a good opportunity to come back into use.
Speaking of the rocky surface of mars, do you know what can be used for crossing sandy planes effectively? Motorcycles. Add into the fact that trenches are hard to build in a sandy environment and you have a pretty good reason to have a motorcycle corps.
Lets also assume that your enemies have motorcycle corps though. How do two motorcycles choose to battle? Well lets go out on a limb and go ahead and give motorcycles front facing missile launchers. Like a miniature rpg launcher with two shots or so, in order to eliminate targets that are hard to penetrate with your normal machine gun. Of course, your motorcycle has an on board computer that helps them aim these mini rockets, possible with a in helmet display so you can confirm your target.
In fact, why not mount a small machine gun in the front of your motorcycle with a helmet tracking software. The gun will automatically adjust to whatever you look at, and then you can shoot in a wider area in front of you, instead of just directly in front. This gives you some amount of firepower if you happen upon an enemy while on a patrol.
Of course, you can have a larger amount of hardware in your martian motorcycle thanks to the lower gravity. In fact, larger, harder, and stronger systems are essentially required to help keep you on the ground. This gives you a lot of play, including bullet proof domes over your motorcycle protecting the driver, especially for recon vehicles or anti cavalry troops.
However, lack of gravity also makes other vehicles a lot more useful, such as tanks that are both lighter, faster, and yet have heavier armor than those on earth.
But lucky for you, high mobility is incredibly important in war, and motorcycles will definitely have uses in recon and support. You could even mess with the whole less gravity thing to make motorcycles that have weapons specialized in anti tank, anti personnel, and anti motorcycle functions. Different motorcycle units could all have specialized roles in a high mobility battlefield where they can navigate the terrain better than other vehicles, be equipped with similar defenses or weaponry as traditionally bigger vehicles on earth, and replace a lot of the functions of aircrafts on earth.
