The new 64-cent Butterfly stamp to be dedicated May 17 at the National Stationery Show at the Jacob Javits Center in New York City — is designed for use on cards that have an irregular shape requiring additional postage.
Participating manufacturers will print a silhouette image of a butterfly on their envelopes, making it easier for customers to understand the new Butterfly stamp or equivalent postage is all that’s needed to mail the card.
The first stamp design in the new series features one of the most recognizable butterflies in North America — the monarch. The stamp will be published as a pane of 20.
The butterfly symbol is universal and will be used on all future stamps for nonmachinable letters. When postal prices increase, USPS will issue a new stamp using the butterfly symbol. The Butterfly stamp silhouette image includes text that reads: “Butterfly Stamp or Equivalent Postage Required.”
USPS requires extra postage, called a “nonmachinable surcharge,” on First-Class Mail letters when an envelope:
•Is square or doesn’t meet aspect ratio.
•Is rigid and doesn’t easily bend.
•Contains items that create an uneven mailpiece.
•Has an address that is parallel to the shorter dimension of the letter (vertical setup).
source: USPS News Link