City of Chicago Municipal Code requires that condominium buildings post contact information for the manager of the association.
13-12-030 Building owner or agent – Posting requirements.
The owner of any building having residential units designed or used for two or more family units or designed or used for sleeping accommodations, other than family units, for more than ten persons shall post, or cause to be posted, in a prominent place in a common area of the building accessible from the public way, or affixed to the building so as to be visible from the public way, the name, address, and telephone number of the owner, his agent for the purpose of managing, controlling or collecting rents and any other person managing or controlling such building.
In the case of self-managed associations, this would be the association or an individual designated as the contact person. Your association may want to set up an association email address and phone number that can be forwarded to the current contact through Gmail and/or Skype.