That's what I teach too. Danger signal's for everyone, maneuvering signals (other than overtaking signal) are for power-driven vessels.
But I might give one blast to a "no looking" port tacker, just to get his attention. As he gets close and I'm unsure of his intentions, then danger signal, and just before you get to where any action on his part will be too late, bail the hell out of there. But regarding sound signals, you're sort of downwind from him, and the sound travels poorly, so no substitute for a good lookout, *especially when you're on port*!