How do the Orc's let the other Orc's know you are Blood-Kin?

The are 3 in Marcarth, two who work forge's in separate locations and never get any visitors or even see each other (to my knowledge) and the one in jail who definitely does not get any visitors. The other Orc strongholds never interact with each other so while one stronghold might make you Blood-Kin the others would not know.

The only true way I can imagine is by courier but I can't imagine the courier regularly stops by their strongholds asking if they've letters to deliver. Plus a title that requires that much trust to be earned seems far more important than any regular note could describe