There are two different types of bicycle share programs in Milano. 

One is called bikeMi and is part of the ATM program, where you can add a nominal monthly fee onto your metro/tram/bus card, giving you authorization to take a bike from designated bike stands throughout the city and return it to another stand. They have this interesting click-into-place system to secure the bikes.  

These bikes also serve as traveling billboards for local cultural events.

Then there are other bicycle shares where you download the app to your phone, and register your "borrowing" of a bike via the phone app. 

These bike share programs (Mobike and OFO) are interesting in that the bikes are not locked into a stand but are considered "dockless". There is a retractable "clamp" that closes into the the back tire, between spokes, and doesn't allow the tire to turn unless someone has 'claimed it' via the app. Steal the bike all you want, but you can't ride it if one wheel won't turn! 

You'll find dockless bikes in the most bizarre places, alone on a sidewalk, in front of the door of the grocery store, waiting for the next rider.