On my 2025 NX Luxury on the heads up display that shows left and right borders of the of the road at times an icon of a back of a car pops up.

Any ideas?

 

Is it only when you're using adaptive cruise? If so, it's to show you that it's tracking the vehicle in front of you based on the distance you've set (the lines between you and the car in the HUD).

 

It basically tells you that you are getting little too closer to the set distance to the car in front of you and your car would like to slow your down or your slow down as you are too close to the car in front, something along these lines