[0] https://wiki.openstreetmap.org/wiki/Draft_Attribution_Guidel...
ODBL ( https://opendatacommons.org/licenses/odbl/1-0/ ) that is a license of OSM data - https://www.openstreetmap.org/copyright ) has requirement to include attribution reasonably calculated to make any Person that views the map aware that Content was obtained from the OpenStreetMap and that it is available under the ODBL License.
Hidden attribution does not fullfill it.
"include a notice associated with the Produced Work reasonably calculated to make any Person that uses, views, accesses, interacts with, or is otherwise exposed to the Produced Work aware that Content was obtained from the Database, Derivative Database, or the Database as part of a Collective Database, and that it is available under this License."