This lovely square postage stamp is what you need to send out postcards for your wedding with the correct amount of postage. These could be Save the Date postcards, RSVP postcards or wedding Thank You postcards. Diamond Monogram Wedding Postage Stamps. Add your monogram initial. Brides wonder sometimes which initial should go on the wedding invitations. You should use the married name initial if it is one or the first letter of your first names if you are using two monograms.