What does the red flag on the side of a US roadside mailbox mean?
Along the roads of American suburbs, small rounded mailboxes stand at regular intervals. White, black, green—the colors vary, but the shape is almost always the same. One detail changes: on some, a small red flag on the side is raised; on others, it lies folded flat.
The standard form of this mailbox was designed in 1915 by USPS employee Roy Joroleman. More than 110 years later, it has changed very little. The red flag on the side is a simple signal: when it is raised, it means, "There's mail to go out today." The mail carrier sees the flag and stops the vehicle. When the flag is down, the carrier passes by unless there is mail to deliver.
The small white USPS mail truck pauses beside the roadside mailbox. The mail carrier steps out, opens the mailbox door, and takes out the letter inside. If the flag is raised, the outgoing mail is collected; if there is mail to deliver, it is placed inside.
Someone places a handwritten letter inside and lifts the flag. A few hours later, a small white truck lingers briefly by the road. After the carrier climbs back in, only the flag folded flat against the side of the mailbox remains. Between the raising and lowering of one red flag, a day passes.