It's a runway marker sign. They are pretty low, and in the grass, and have breakaway mounts. This sort of thing: https://blog.klm.com/assets/uploads/2015/08/Signs_7.jpg
The aircraft would have been way off center of the runway, with the left wing literally dragging the ground.
JFK runway 31L is 200 feet wide, an A321 has a wingspan of 112 feet. The wings are 12 feet from the ground at the fuselage, and maybe two feet higher than that at the wingtips. The photos[1] show heavy abrasion under the left wingtip, presumably it was dragging the ground.