Two questions, where are motorcycles supposed to be parked, if not on the street, and where are there alleys so narrow that you cant fit a scooter through it? Is that technically even an alley?
I would definately fight this. If you just leave the scooter, you will still be responsible for the fees which will eventually be sent to collections. DPW is notorious for ticketing scams, but luckily there is an appeal process.