Residential curbside mailboxes come in a variety of colors, shapes, and sizes. One trait they all have in common is the small pivoting flag attached to its side. Just as the United States Postal Service enforces regulations for these mailboxes, there are also regulations in place for the signal flag attached to it.
A mailbox signal flag is required for all privately-owned traditional, contemporary, and locked mailboxes.
All mailbox signal flags must be attached to the right side of the mailbox when facing it from the front. The flag is to be raised when outgoing mail is present in the mailbox. The flag is to be lowered by the postal worker after outgoing mail is picked up.
A mailbox signal flag can be any color other than shades of green, white, yellow, blue, or brown. The flag color recommended is orange or red with the flag's color having a complete contrast to that of the mailbox's color scheme.
The signal flag cannot weigh more than 2 pounds. The flag can have an automatic lowering mechanism attached to the box as long as it does not pose an interference to the postal worker's delivery routine.