what is the symbol I just saw on one of my notifications that is a small white triangle with circles behind it?
In the comments, @Lizzan discovered that it might be the AirDrop icon, you have seen.

I just want to assure you that AirDrop neither records you or plays some recording. It is meant exclusively for transferring files from one device to another. An AirDrop notification would be about someone within your vicinity trying to send you something. You would have been prompted to accept or reject the file.

On the other hand, AirDrop doesn't have anything to do with iPhone Mesages, nor does it usually appear in the top right corner as far as I know. Therefore I think it might be that the icon you have seen is actually the new AirPlay icon, which is very similar to the AirDrop icon. You can see that icon here:



Note that the icon is displayed in the top right corner of the media controls, and reachable from the control center that you can access from everywhere on your iPhone - including the Messages app.