The sender should mark postcards Par Avion or affix Label 19–A, Par Avion Airmail, or Label 19–B, Par Avion Airmail, on the left side on the front.
The right half of the address side of a card must be reserved for the address of the addressee and postal notations or labels.
The sender may use the left half of the address side of the card and the reverse side for a message or permissible attachments. The sender must use the upper–left half of the address side for his or her return address. (Unless they bear the name and address of the sender, undeliverable cards are disposed of in the country of destination.)
The following may be glued on the left half of the address side of a card, or on the side opposite the address side, if they are made of paper or other thin material and adhere completely to the card:
- Clippings of any kind.
- Illustrations or photographs.
- Labels other than address labels.
- Stamps of any kind, except stamps likely to be confused with postage stamps, must not be placed on the address side of the card.
- Address labels or address tabs that may be glued to the address side of the card.
The following must not be attached to cards:
- Cloth, embroidery, or spangles.
- Samples of merchandise.