I tried to figure it out but haven't seen anything underneath it yet (took a quick glance). I was too focused on getting that freaking rear bumper off lol. The screws look old, and they aren't completely screwed in, almost like you could slide some kind of bracket behind them for something that would be mounted on the inside of the car.
Probably not important to you the current owner.. Someone who owned it before had something secured with them and there doesn’t seem to be anything for them to hold on to now. The only thing they are doing now is keeping the screw holes in the floor filled..