After the honk I saw them in the FSS interface and in the Navigation panel. Although I am not 100% certain that this was the case with the first one I discovered. I think I had to use the dial on the FSS to find it. Perhaps someone with more experience can chime in here.
I just found 2 more Notable Stellar Phenomena about 1,700-1,800Ls away from the main star.
One is Flavus Metallic Crystals and the other is Roseus Metallic Crystals.
Roseus Metallica Crystals
After the honk they appeared in the Navigation Panel. In the FSS interface they appeared as signal emissions in the lower scale until I dialed in to the signal, found them on the screen and zoomed in. Then they appeared as an exclamation mark icon.
Those are all systems which have been discovered before. I've yet to find an undiscovered system with a Notable Stellar Phenomena.