Need to know what this means and if there's anything supposed to be hooked to it

Post a photo.

Odds are it is a jump start reminder to ground to an engine bolt.

Sounds like where they want you to hook up the negative jumper cable when giving or receiving a jump start. It's actually dangerous to hook up directly to the battery! Batteries can produce hydrogen gas which can be explosive. Batteries have exploded from just the small spark that sometimes happens when hooking up jumper cables. Hope that helps! Jim