Semaphore or signal flag.
Yes and yes.
No, mailbox flags do not have to be red in order to be effective. The purpose of a mailbox flag is to indicate to the postal carrier that there is outgoing mail to be picked up. The color of the flag is not a requirement for its functionality.
Mailbox?
In the US, when the flag is up it means there is outgoing mail in the mailbox to be picked up by the letter carrier. This alerts the letter carrier to stop at the mailbox even if s/he has no incoming mail to leave for the addressee. When you get ready to mail a letter, leave it in the mailbox and raise the flag. When the letter carrier arrives s/he will take the mail you left in the mailbox, leave any mail s/he might have for you and lower the flag. The flag can also serve as an indication the letter carrier has come and left mail, but it's generally thought inconsiderate to use it for that purpose alone because if the letter carrier has no mail for you it forces him or her to make an unnecessary stop.
The name on the mailbox in "The Grapes of Wrath" was Joad.
The rules for mailbox flag usage are that you should raise the flag to signal outgoing mail for the postal carrier to pick up, and lower it once the mail has been collected. It is also customary to raise the flag when you have incoming mail to be picked up. Remember to only use the flag for its intended purpose and not as a decoration.
Pole Dancing
Old Glory.
Yes, as long as it isn't stolen mail. No, it is illegal, even to place a flyer on the flag. The mailbox is US Government property.
a linked in mailbox, your welcome
The Alabama state flag has a Crimson cross on a white field. It is also called the confederate battle flag.
Old Glory