Arrow and lines

I took this photograph on a cold November night at the new Pembury hospital. I'd taken a few of the building before noticing this arrow on the ground.

What I'm not sure of is where the wavy white lines came from. I'm assuming that I didn't use the self-timer and so the camera moved as I took the photograph. The camera then settled on the tripod for the rest of the 21-second exposure which is why everything else is sharp.