Snail mail may not be as popular as before e-mail and social media, but people still mail letters and cards--and that's an opportunity for marketing.
Planning a wedding? Many engaged couples look at every detail, including the stamps on their invitations, as the New York Times points out. The USPS has its own standard love or wedding stamps (top) but authorized marketers such as Zazzle also offer personalized stamps (just above).
India Post is not only offering personalized stamps, the Mumbai General Post Office provides a photographer to take the photo of you and your sweetheart (or anyone else whose likeness will be on the stamp). Wedding stamps are popular but so are "new baby" stamps.