Which of the following is considered a non-postal stamp?

Migratory bird stamps are recognized as non-postal stamps because they serve a different purpose than regular postage stamps. These stamps are specifically issued for the conservation of migratory birds and are used primarily as a means to raise funds for wildlife protection and habitat restoration. They do not serve as payment for postal services, which is the essential function of postage stamps that are used to send letters and packages.

In contrast, postage stamps, international reply coupons, and stamps for parcels all directly relate to mailing services. Postage stamps are used to pay for the delivery of letters and parcels. International reply coupons enable senders to pay for a reply from another country, ensuring that the recipient can respond without incurring postage costs. Stamps for parcels function similarly to enable the shipping of parcels domestically and internationally. Therefore, the distinct purpose of migratory bird stamps classifies them as non-postal.