Updated June 1st: First day postmarks:
Standard 4-bar FIRST DAY OF ISSUE
Digital Color Postmark:

from the Postal Bulletin May 27th:
On June 1, 2015, in Kansas City, MO, the U.S. Postal Service® will reissue the Wedding Cake two ounce rate mail-use stamp, (Non-denominated priced at 71 cents), in one design, in a pressure-sensitive adhesive (PSA) pane of 20 stamps (Item 589600).

The stamp will go on sale nationwide June 1, 2015.

The Wedding Cake issuance, first introduced in 2009 and sold at the two ounce stamp price, accommodates the heavier weight of an invitation, as well as other mailings such as oversize cards or small gifts that require extra postage. The stamp art features a photograph taken by Renée Comet of a three-tiered wedding cake topped with white flowers. Pastry chef Peter Brett created and designed the cake. The words “Two Ounce” on the stamp indicate its usage value. Like a Forever® stamp, this stamp will always be valid for the rate printed on it. The initial price and value for this stamp is 71 cents. Art director Ethel Kessler designed the stamp.

How to Order the First-Day-of-Issue Postmark:
Customers have 60 days to obtain the first-day-of-Issue Postmark: by mail. They may purchase new stamps at their local Post Office, at The Postal Store® website at http://www.usps.com/shop, or by calling 800-STAMP-24. They should affix the stamps to envelopes of their choice, address the envelopes (to themselves or others), and place them in a larger envelope addressed to:

71¢ Wedding Cake Stamp
Cancellation Services
8300 NE Underground Drive, Pillar 210
Kansas City, MO 64144-0001

After applying the first-day-of-Issue Postmark:, the Postal Service will return the envelopes through the mail. There is no charge for the postmark up to a quantity of 50. For more than 50, customers have to pay five cents each. All orders must be postmarked by July 31, 2015.

There are five philatelic products for the Wedding Cake stamp issue:

• 589610, Digital Color Postmark Keepsake, $16.95.
• 589616, First-Day Cover, $1.15.
• 589621, Digital Color Postmark, $1.86.
• 589631, Stamp Deck Card, $0.95.
• 589632, Stamp Deck Card with Digital Color Postmark, $2.21.

Technical Specifications:

Issue: Wedding Cake Stamp
Item Number: 589600
Denomination & Type of Issue: Two Ounce Rate Non-Denominated, Mail-Use
Format: Pane of 20 (1 design)
Series: Weddings
Issue Date & City: June 1, 2015, Kansas City, MO 64108
Designer: Ethel Kessler, Bethesda, MD
Art Director: Ethel Kessler, Bethesda, MD
Typographer: Ethel Kessler, Bethesda, MD
Photographer: Renée Comet, Washington, DC
Modeler: Donald Woo
Manufacturing Process: Microprint, Offset
Printer: Banknote Corporation of America/SSP
Printed at: Browns Summit, NC
Press Type: Alprinta 74
Stamps per Pane: 20
Print Quantity: 30 million stamps
Paper Type: Phosphor Tagged Paper, Overall
Adhesive Type: Pressure-sensitive
Processed at: Banknote Corporation of America, Browns Summit SC
Colors: Cyan, Magenta, Yellow, Black PMS 874, PMS Warm Gray 9
Stamp Orientation: Vertical
Image Area (w x h): 0.76 x 0.87 in./19.18 x 22.01 mm
Overall Size (w x h): 0..91 x 1.19 in./23.11 x 30.22 mm
Full Pane Size (w x h): 5.43 x 5.64 in./137.80 x 143.12 mm
Press Sheets Size (w x h): 10.85 x 22.54 in./275.59 x 572.52 mm
Plate Size: 200 stamps per revolution
Plate Numbers: “S” followed by six (6) single digits
Marginal Markings: Front: Plate numbers in two corners of pane
Back: © 2008 USPS • USPS logo • Plate position diagram • Barcode (589600) in upper right and lower left corners of pane • Promotional text

From the USPS May 26th:
The Wedding Cake issuance, introduced in 2009 and sold at the two-ounce stamp price, accommodates the heavier weight of an invitation, as well as other mailings such as oversize cards or small gifts that require extra postage. The stamp art features a photograph taken by Renée Comet of Washington, DC, of a three-tiered wedding cake topped with white flowers. Pastry chef Peter Brett of Washington, DC, created and designed the cake. The words “TWO OUNCE” on the stamp indicate its usage value. These Forever stamps will always be equal in value to the applicable price for the price category printed on them, at the time of use. The initial price and value for this stamp is 71 cents effective May 31. Art director Ethel Kessler of Bethesda, MD, designed the stamp.

From the USPS May 18th:
The Wedding Cake issuance, first introduced in 2009 and sold at the two-ounce stamp price, accommodates the heavier weight of an invitation, as well as other mailings such as oversize cards or small gifts that require extra postage. The stamp art features a photograph taken by Renée Comet of a three-tiered wedding cake topped with white flowers. Pastry chef Peter Brett created and designed the cake. The words “Two Ounce” on the stamp indicate its usage value. These Forever stamps will always be equal in value to the applicable price for the price category printed on them, at the time of use. The initial price and value for this stamp is 71 cents. Art director Ethel Kessler designed the stamp.

The first day of issue is June 1, without a ceremony. The city is Kansas City (Stamp Fulfillment Services).