USPS Outgoing Mail Tag

For postal workers who deliver to apartments or trailer courts with large multi box community mail units. Most of these units have no "outgoing" flag to indicate the customer has outgoing letters. In these cases, it's easy to miss an outgoing letter. To help my sister (a mail carrier) deal with this, I made her bunches of these tags. She hands them out to all of her customers in these units. When they have an outgoing letter, they clip one of these onto the edge of a letter. Now it's obvious when there is outgoing mail and the customers are much happier. Most leave the tag in the box at all times and use it as needed. When she picks up the mail, she returns the tag to their box.
The tags have an "envelope & arrow" indicator on the side showing how to use them.
It seems to be working. I'm printing her another batch of them now.