Eh. Those look like anti-pee systems to me. I bet it was an official take "to reduce crime" - but those things are all slanted down, to push pee on your foot. And when I need to pee corners always catch my eye.
"However, the "antibandito humps" had a second usefulness, so much so that it received a second name: that of the "pissotte" or "pissabraghe": in addition to preventing criminals from hiding from their prey, it's said that the inclined casts of mortar also had the task to maintain a certain public decorum and therefore prevent Venetians from urinating in the corners of the calli."
I suspect it was the primary purpose, and anything else sounds like cleaned up reasons for publication.
As it wouldn't be hard to stand on one in the shadows.