Parking brake. The lever (on the right side of the original picture), flips down to release.
When in stock form, there's no lock on this lever, so someone could theoretically walk up, flip the lever, and roll your Ryker away.
The accessory lock slides a metal pin into the lever when the key cylinder (silver circle in the middle of the pic) is turned, thus preventing the lever from moving.
Installation requires you to drill a hole the same size as the cylinder circle. Looks like the drillbit Beanz used snagged a little bit on the plastic, making the edge of the hole not as clean as he would have liked.
I agree with everyone else.....no one else will else will notice but Beanz....
Later,
EV