What does an "X" in a black circle in the status bar mean? Just to the left of my battery percentage, there is a x inside of a circle in the status bar. I've never seen this before and was hoping someone could explain this! Thank you!

Edit: Here is an screenshot:
Sorry for the late reply, but thank you to everyone for your help! I found the problem was a theme installed called 'Veexillum' and the actual icon is just orientation lock! Thanks again to everyone!