A woman from Chicago called in last week wondering about the moral dilemma of “saving” a parking space that she shoveled. Tom & Ray said the “Law of the Jungle” was in effect and that putting a garbage can or a lawn chair in place was perfectly acceptable.
I say B-O-G-U-S! It’s a public street and a person’s labor does not equal ownership. Sorry, boys, but you gave bad advice on this one.
Thats why I work first shift… When I get home at 4 everyone else is still at work, so I don’t have to fight for the space I shoveled. It’s still empty from when I left for work at 6. 
It would be bad advice in most places, but both Chicago and Cambridge have strong local customs of “you shovel it, you can claim it.” (You do have to put an object, such as a chair, in the space to stake your claim.) Even in those cities, there’s some disagreement – the custom is very strong in some neighborhoods and almost absent in others.
However, in my Chicago neighborhood, it was so much part of the culture that if locals spotted someone removing the Object and parking in a Previously Shoveled and Claimed Space, they would get in the intruder’s face about it even though it wasn’t “their” space! (After a couple of snowfalls, you got to know which face went with which piece of furniture.) It violated a social norm and people objected, kind of like challenging a dog walker who let their Great Dane do his business in the middle of someone’s lawn.
The advice was sound. It may not be legal wise, but moral wise anyhow. How fair is it to take advantage of a spot someone else shoveled out and drive by the unshoveled areas? It’s not fair & could be dangerous in my neck of the woods…for your car anyhow. You could come back to find a couple of flat tires on your car. A little “street justice”! 
So then , what is the protocol when there’s nothing to shovel ?
I’ve never had to deal with this ( I can fit 4 trucks in the back yard driveway and still have room for one in the front driveway ) but I’ve seen “parking wars” on tv and can’t imagine playing parking spot roulette every single day.