The cover sheet depicts a bird in flight, while the inner cards use only a feather to carry the theme through. This idea can be applied to almost any object that is beautiful or significant to you. For example, a bouquet may embellish a cover card, and a single peony from the bouquet will adorn subsequent cards.
Sometimes a simple, well-chosen symbol says enough. An icon can be just aesthetically pleasing, as a botanical image, below.
Icons also can have inherent meanings, such as the interlocked wedding bands (left), or the crown (right), which reminds guests the wedding will be held in a castle.