This is a Front End Lowering Strap
This strap attaches to a brake caliper mount on either side of the motorcycle and over the frame. This allows you to then "pull" the strap to the desired height and let go. It basically works just like a motorcycle tie down does, and has a release button to press to put the bike back to the stock height when riding on the street.
This strap is intended for off road use only, not for use on public streets or highways. Always observe safety first.