Ok here's my plan to create a covert urban orchard. I have used my city's GIS to locate all of the flowering crabapples in town. I will start close to my house and graft onto a few of the branches using apple scion wood from my own tree pruning. I figure it will be easier to use the existing trees and graft rather than attempt to plant new trees and hope they don't get mowed over or eaten by animals. If the city employees find out about them, they'll probably get chopped off. I'm ok with that, I just need to use the trees that they won't find. I can use brown elastic that will more or less camouflage the graft union. If I use a bright neon-colored elastic, it'll be easy to spot and likely removed.
I'd probably feel bad about doing this if I were to just abandon the grafts and let the apples fall and make a mess. But as long as I keep the trees close to my house, I'll be able to take care of any pest management and harvesting just as I do for my own trees. I think of it as an extension of my own backyard orchard.
The dream is to one day be able to harvest enough fruit to provide to the local food bank or a homeless shelter.