What is this emblem thing on my screen?

Help me out here.
https://i.ibb.co/F8d6Mhs/image.jpg
Never mind...

That means you have Shield Oath on.

Right now it's not particularly useful, but when you hit level 52 and learn Sheltron, that gauge will expand to display a number from 0~100, representing another resource you can spend to use a couple new skills. Also, the icon will be blue instead of yellow when you have Sword Oath on.

Thank you. I turned it off. ;D

You might not want it off.
Try simple mode instead.

To be clear, shield oath itself is very useful. The gauge itself is just not super useful at that level in only serving to remind you that you have it on.

You need to go into your HUD and move it where you want it.