Optical communication in daylight

Earlier, I noticed the the reflection of the sun from my watch face on a distant wall. This got me thinking of heliographs. These were used to send Morse code messages in sunny countries. I think ranges were remarkable.  See https://en.wikipedia.org/wiki/Heliograph. I seem to recall ranges were up to 80km. The best DX (line of site) was 295km.  Basically, the sun's reflection was obstructed to send CW.

My mind turned to QRSS beaconing. For this to be possible it would be necessary to divert the beam when the QRSS was not on. One possibility would be to have a loudspeaker with a mirrored sheet (kitchen foil?) over it with a tone keyed.  It would also be necessary to have a receiver that was optimised for daylight.  I have no idea how good this would be. 

I guess the same idea could be used for speech. The mirror would be deformed as speech was said. I seem to recall there was a 19th century patent for this called the Photophone. For speech I guess one could simply speak against the metal foil mirror.

I would imagine an optimised system could be used for over-the-horizon (NLOS) tests. Sadly, my health these days means I can only dream about this. It may already have been tried.