Where: At the entrance to a large communal apartment which is home to more than 20 people, in a prestigious neighborhood in the historic center of St. Petersburg.
What: Around the doorbells one can still see bits of paper indicating how many times to ring for each resident. This is for the so-called "common" doorbell.
This type of system is often combined with separate bells for certain residents. Next to such private doorbells there is usually a note indicating whose it is. In some cases it is assumed that potential guests know this already (see other doorbells on the door of this same apartment).