According to the Roosevelt Island Operating Corp (RIOC)
Notification issued 5/7/2014 at 4:00 PM. As a reminder, unauthorized postings and advertisements are not permitted on Main Street's bus shelters. Posting is allowed on RIOC's Main Street kiosks, which are cleaned on the 1st and 15th of every month. To view RIOC's full Advertising and Posting Standards for the Red Buses, Tram and kiosks, please visit http://rioc.ny.gov/pdf/AdvertisingPolicy.pdf .It is unclear what makes one bus shelter sign authorized
Roosevelt Island Operating Corp Advisories Group
Image Of Riverwalk Bus Shelter With Signage For RIOC and FDR Park
and another not.