In other words: we already have lots of things that measure photons. You see things on two totally different media it's a lot more compelling than just one.
Or we can all just think big thoughts at the same time... https://en.wikipedia.org/wiki/Calling_Occupants_of_Interplan...
Also, if you're sending out photons from a planet, chances are there's a local star nearby. Stars tend to be a broad-spectrum photon source, which is going to make it tough for receivers to decode the intentional signal.