parkway tic-tac-toe

I've noticed this before but didn't really give it much mind...but along the fairfax county parkway there are these giant (five feet long at least) gray X's that are too wide to be duct tape but look like they have the strength of the all-mighty duct tape nonetheless...anyways I kept looking for the O's in the big majestic game of tic-tac-toe but thus far haven't found one...