Helicopters flying over airport

Are they allowed to fly over airports??
Why and how often?
Do they have callsigns?

I saw one flying over JNB today when driving to work.

Yes they are but like a plane they have to have permission it’s like a plane flying low over an airport and yes they do have call signd

Helicopters are not allowed to enter airports unless someone important told them they can …

???
Most helicopters are based out of and land at airports…

Yes they do unless told otherwise …