Custom Wedding Invitation Envelope Postage Stamps - Browse an array of custom Customizable Wedding Invite Envelope Postage from the wedding postage designer at Artistic Postage. Thank You Triangle Stickers And Envelope Seals. These elegant custom green and purple thank you stickers are perfect to use as envelope seals for thank you cards. Use them on the outside of a wrapped gift or gift bag. Great for thanking your guests for showing up at your wedding, anniversary, birthday party, graduation, bridal shower, baby shower, Holiday party and any other special occasion.