Has there ever been a case of adding new Handicap parking signs on weekends? (I just got a ticket)?

I parked near the washington monument today and got a handicap parking violation of $250. I didn't see that sign there when I parked in the AM(nor did any of my 4 friends in the car with me), and there were at least 5 cars there with me, and they all got tickets. My question is, did we really all not see it? or have you ever heard of people adding new handicap parking signs on sundays?