Maybe not new: preventive measure before Macy's Fireworks

[ka jowct]

My work route over the weekend included Avenue C along the FDR drive. The fireworks were n the East River this year. I noticed perhaps 2 days before the big event that mailboxes in that area had been fitted with locks and a warning notice. On the 5th, the locks and notices were gone. It makes sense to do this, but I have no idea how long this has been going on. Anyone know? Is it SOP for parades as well?