My primary means of transportation is a motorcycle. Last year, I put about 36,000 miles on bikes. I ride year round. I also wear ATGATT....All The Gear, All The Time. Protective jacket, pants, gloves, helmet, and boots, all motorcycle specific.
I've discovered a few things about firearms and motorcycles. It is pretty hard to operate both at the same time. I rarely get on a bike without protective gloves on. Few protective gloves offer the dexterity to draw and operate a handgun. Holster retaining systems, trigger guards, safety switches, etc. are almost impossible to safely or efficiently use with gloves on. Removing a glove while underway on a bike is no small feat. It is hard for me to imagine a situation I would encounter that would be made better by drawing a weapon with either hand. My strong hand is my right hand, which also runs the throttle. My left, weak side hand, once it has a handgun in it, will no longer allow me to operate the front brake, which offers the majority of my stopping power. Basically, by drawing a weapon, I have relinquished over half of the control of the bike. Re-holstering would be a bit difficult when adrenaline, confusion, fear, shock are all running through my brain and veins. I'm pretty much resolved that any weapon use is limited to stopped or off the bike use. Road rage incidents are better dealt with using either the brakes or the throttle. Drawing a weapon in traffic may relay the wrong message to an onlooker who may feel threatened, and remove the threat with their SUV. Food for thought. I can't imagine any firearm being an effective defense tool on a moving motorcycle. Once stopped, it would take some quick action to make yourself ready to use a firearm. Dropping a bike to address an attacker is easier said than done. Often, the rider goes down with the bike, a disadvantage I wouldn't need right then. Evasion would be my first and foremost option.
If you are carrying as a fashion statement, consider the risks in a get off. Wearing the right riding gear usually allows for a slide to a stop. An exposed holster is providing for something to catch on the ground and send you into a tumble you might not of otherwise encountered. Where is the payoff for the risk?
On a side note...will your holster retaining system withstand the impact, or number of impacts that could happen in a crash? If you leave the scene in a meat wagon, who finds and tends to your weapon, if it slides down the road or was thrown into the ditch? Just things to consider.