I don't ride often, but I use a leather shoulder holster for my Sig under a jacket. Doesn't print or show, and it's secure. Doesn't really meet your desire to have a holster you can easily (read: discretely) remove and stash somewhere...
In the car I use holsters that I can discretely (you're right, better word for what I mean than "easily") remove or put on while in the car due to MD laws. If I am wearing an empty holster I am likely to have the car searched should I be stopped in MD and the officer sees the holster. MD transport laws are strict. Home to the range (and back), home to a gunsmith (and back), to and from dog training or hunting, and from the store to home (at time of delivery) are about all that are legal. Even stopping on your way home for a burger, gas or just to use the bathroom are all illegal. The state AG is on record as saying (in a letter- it wasn't just on the cuff remarks, it's official policy) that the federal law protecting interstate travel with firearms only applies to people going through
MD and does not apply when the origin or destination is MD (so since I start in MD when leaving, and my destination is MD when returning, it wouldn't apply). I recently applied and became a "Designated Regulated Firearms Collector" in the State of MD so I can now also legally transport some or all of my guns to hold a "public or private exhibition", so I am also legal if I go to someone's house where I'm going and show them my guns (that status also allows me to ignore MD's one a month law).
All that said as to why I usually am very careful about the type of holster I use, I may go the easy route when using the motorcycle and ride there with an open holster and simply put my gun in the holster once I get there. Now that I'm a "designated collector" (i.e. I filled out a notarized form stating that I am a collector, the state ran another background check on me and I got a letter stating that I was accepted), I am OK even if I return home at hours a range would be closed since I could be coming home from a friend's house (and MD is bad, believe me, I'm covering my bases and at some point in the trip I am going to a friends or family member's house and asking if they want to see my guns, if anyone lives near where I'm traveling). Still, since I won't be able to slip into the car to discretely place the gun in the holster, I may still travel without the holster on my person. I can have the holster and gun in some kind of bag (small duffel, backpack, whatever) and at my first stop out of MD I can use a public bathroom to put on my holster and place my gun in the holster.