PLB AIS Test: Advice Needed

[HeinSdL]

The other day I needed to test my PLB AIS devices, while in an Italian marina. After activating them one by one using the test button (and one was indeed U/S) the marina manager came over to inform me that the coast guard had called them to enquire if all was well. Apparently not all AIS receivers correctly display the 'test' message on the screen.

So the question I have is, what would be the correct message to broadcast on the VHF to make other AIS users aware (should they be listening in on C16) that it is a test?