From OpenStreetMap Wiki
Definition of the proposed parameter Mandatory, in the context of cycleways.
Note: This parameter is not yet generally accepted!
|yes||Indicates that the cycleway is Mandatory - motor vehicles are not permitted to enter. Indicated physically by a solid white line|
|no||Indicates that the cycleway is Advisory - motor vehicles are permitted to enter. Indicated physically by a dashed white line|
Usage, see taginfo: