open mailbox with raised flag

An open roadside mailbox (Letterbox, Postbox) with its signal sign raised and a letter in its open slot. Usually depicted in blue or gray with a hazard sign and a white envelope, although Google's envelope was previously yellow. Used for various things relating to postal deliveries and email. Indicates in the United States that there is mail (postal) for pick-up. May also indicate that delivered mail has been delivered.