It's the phone telling you it restarted...... Not sure why this is done, but apparently it has been coded in for several models now. This is my first Samsung since the S5. It was annoying me to no end, with the symbol and setting off my notification tone when I restarted the phone... Like I didn't know I restarted the phone in the first place.
Go into Settings - Hit the magnifying glass to search- search: system ui - hit the one with the P symbol- Notifications- go down to fbe_channel_name - put it to silent and minimized. Problem solved.. No more P symbol and no more tones going off.
I believe the P notification is not only telling you the phone rebooted, but that you have to unlock the device to complete the bootup process. My S10e will not accept a fingerprint for the first unlock, so I could not capture a screen shot. After unlocking the device the cell carrier and weather widget finish loading.