I wouldnt be suprized if it was originally Marks moped that got stolen and used until someone broke it and was kind enought to return it to the alley.
In all seriousness, Mark is a cool guy and I highly doubt he would steal something.
Also as a moped rider I cannot understand how someone would bring themselves to steal a moped. I mean imagine yourself coming out of a coffee shop or something. You would be devistated if your moped was gone.
I trust Mark to do the right thing with the bike, try and find the owner and if that doesnt work part that bitch out. At least then you will be helping the moped community.