On a neighborhood e-mail list that I subscribe to, a thread has begun in which people are protesting against those neighbors who don't shovel their sidewalks. One writer links to Ask Chicagoist, which quotes the Chicago municipal code (and I haven't confirmed this quote):
The snow which falls or accumulates during the day (excepting Sundays) before four p.m. shall be removed within three hours after the same has fallen or accumulated. The snow which falls or accumulates on Sunday or after four p.m. and during the night on other days shall be removed before ten a.m.
I agree with the code, and with my fellow e-mailers, on this. Snowy sidewalks are no big deal in themselves, but they become icy sidewalks after they've been walked on for a while, and those things are dangerous.
When it's necessary to shovel on Shabbat, I always do so, wearing socks on my hands as a shinnui (and this was before I saw this quote from the code). I haven't asked a rabbi about this, and this is out of respect for the rabbinate--I want to save them the embarrassment of possibly giving the wrong answer.
As a side note, I once told a friend, former and (I hope) future havrusa and/or hevruta, and ethical adviser about this. He (who lives in an apartment where the landlord is responsible for shoveling, so it's not his problem) said he thought this a fine idea. Since it's just me, he said, I should do it without any distinctive Jewish accessories visible. If, however, I were R' Gedalia Dov Schwartz, av beit din of the RCA and the Chicago Rabbinical Council, who lives a few blocks away, he'd advise me to do it looking like I was R' Gedalia Dov Schwartz so everyone would know it's OK. I take his point, although I should point out that if I were R' Gedalia Dov Schwartz, I wouldn't need his advice.