From the U.S. Postal Service announcement on November 17, 2020:From the USPS: The new Mystery Message stamp will put your sleuthing skills to the test. Featuring bright colors and interesting shapes, the stamp design is a visual riddle spelling out a message. Each colorful square contains a letter in an interesting pattern. The patterns, though seemingly random, were carefully placed so that when put all together, the message reads, “MORE THAN MEETS THE EYE!” Art director Antonio Alcalá designed the stamp.

Additional information will be posted below the line, with the most recent at the top.

Updated August 2nd:
Here are the Scott catalogue numbers for this issue:
The regular stamp is 5614. The imperforate variety is 5614a.

Updated June 17th:
Here are the postmarks for this issue:The Digital Color Postmark measures 2.98″ x 1.29″The B&W pictorial postmark measures 2.76″ x 1.21″

Updated June 17th from the Postal Bulletin:
On July 14, 2021, in Washington, DC, the United States Postal Service® will issue the Mystery Message stamp (Forever® priced at the First-Class Mail® rate) in one design, in a pressure-sensitive adhesive (PSA) pane of 20 stamps (Item 480700). This stamp will go on sale nationwide July 14, 2021, and must not be sold or canceled before the first-day-of-issue.

The new Mystery Message stamp is designed to put your sleuthing skills to the test! Featuring bright colors and interesting shapes, the stamp design is a visual riddle spelling out a difficult-to-discern message. Each colorful square contains a letter in an interesting pattern. The patterns, though seemingly random, were carefully placed so that when put all together, the message reads, “More Than Meets the Eye!” The reverse side of the pane provides the solution. Art director Antonio Alcalá designed the stamp.

No automatic distribution.

How to Order the First-Day-of-Issue Postmark:
Customers have 120 days to obtain the first-day-of-issue postmark by mail. They may purchase new stamps at their local Post Office™ or at The Postal Store® website at usps.com/shop. They must affix the stamps to envelopes of their choice, address the envelopes (to themselves or others), and place them in a larger envelope addressed to:

FDOI – Mystery Message Stamp
USPS Stamp Fulfillment Services
8300 NE Underground Drive, Suite 300
Kansas City, MO 64144-9900

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. There is a 5-cent charge for each additional postmark over 50. All orders must be postmarked by November 14, 2021.

Technical Specifications:

Issue: Mystery Message Stamp
Item Number: 480700
Denomination & Type of Issue: First-Class Mail Forever
Format: Pane of 20 (1 design)
Series: N/A
Issue Date & City: July 14, 2021, Washington, DC 20066
Art Director: Antonio Alcalá, Alexandria, VA
Designer: Antonio Alcalá, Alexandria, VA
Modeler: Sandra Lane / Michelle Finn
Manufacturing Process: Flexographic, Offset, Microprint
Printer: Banknote Corporation of America
Press Type: Gallus RCS
Stamps per Pane: 20
Print Quantity: 20,000,000 stamps
Paper Type: Phosphor, Block Tag
Adhesive Type: Pressure-sensitive
Colors: Cyan, Magenta, Yellow, Gray PMS Cool Gray 5C
Stamp Orientation: Vertical
Image Area (w x h): 1.085 x 1.085 in. / 27.559 x 27.559 mm
Overall Size (w x h): 1.225 x 1.225 in. / 31.115 x 31.115 mm
Full Pane Size (w x h): 5.8375 x 7.12 in. / 148.272 x 180.848 mm
Press Sheets Size (w x h): 14.24 x 23.35 in. / 361.696 X 593.09 mm
Plate Size: 160 stamps per revolution
Plate Number: “B” followed by four (4) single digits in bottom two corners
Marginal Markings:
Front: Header: Mystery Message • Plate number in bottom two corners
Back: ©2020 USPS • USPS logo • 2 barcodes (480700) • Plate position diagram (8) • Promotional text • “More Than Meets The Eye!”