Looks like your phone doesn't recognize the SIM card or something....don't hold me to that, I could be wrong but that's just what came to me off of the top of my head.
Rebooted my phone and it went away. But don't know what it meant, like I said phone was working fine as far as I could tell. Was using data and making phone calls.
If it was the SIM not being read--it wouldn't show any network connection (i.e., 4gLTE) but a circle with a line through it (pop your SIM out and you'll see). I would check the icon glossary in the user manual if you really want to know. Cheers