Yes I've found a few of those - in fact there were some in the system I just left. WikiFandom has an article about them here:
Notable Stellar Phenomena are a type of signal source found in certain star systems, at stellar or planetary lagrange points or in Planetary Ring Systems. Each instance usually features a colorful Lagrange Cloud surrounding various organic or inorganic entities. These entities can be scanned by...
elite-dangerous.fandom.com
They are classed as organic and I think they show up in the Codex along with the bios found on planet and moon surfaces. In my Asp X though, I've only been able to scan the ones I found with the Short Range Composition Scanner but not been able to actually collect any samples, as I have no room on the ship to fit a Research Limpet Controller.
After I've scanned one of those a Codex message will pop up saying I have a 500CR or something reward, but I checked EDDiscovery afterwards and nothing shows up there to indicate any payment I might get from VIsta or Cartographics. (I'm not sure which one of those is where you sell them.) Maybe If I could collect samples as well they will show up, not sure.
So, at least as far as I'm concerned with my Asp X loadout, I've now come to the conclusion that it's not worth my time travelling to those signal sources when I can only scan them and not collect.