This property denotes a service as either public or private. 
   Namespace:   Autodesk.Revit.DB.ExternalService  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2014 
Syntax
Remarks
A public service can be executed by anyone, while a private service can be execute only by the caller who registered it (the owner of the service, typically), or by someone who has access to the service's execution key.
Unless specified otherwise, all services are created as private by default.