What is a good way for an astrally projected mage to communicate to someone in the physical world??

For example if a team of runners is infiltrating a corp. building and an astrally projected mage is running overwatch on them what would be a good way to communicate with the team in the physical world.

Can an astrally projected mage "materialize" in the physical world like a spirit can??

Would the mage have to use an illusion trid spell to create a "neon sign or writing on a wall" to pass a message along??

Astrally projecting mages can manifest (not materialize). They become visible and audible but are still non-corporeal and cannot interact with physical objects. So the mage can just talk to his buddies. Or give hand signals, I guess.