From the U.S. Postal Service announcement on November 17, 2020:From the USPS:The four fun designs on this new pane of 20 stamps invite interactivity with dozens of self-adhesive accessories that personalize your cards, letters and envelopes for delighted recipients. Decorations include hearts, hats, voice balloons, flowers and thought bubbles. Art director Antonio Alcalá designed the pane with new illustrations by Elise Gravel.

Here are the Scott catalogue numbers for this issue:
5636 Pink and Red Monster
a. Imperforate
5637 Four-armed Monster
a. Imperforate
5638 Tentacled Monster
a. Imperforate
5639 Red-headed Monster
a. Imperforate
b. Horiz. or vert. strip of 4, #5636-5639
c. Imperforate strip of 4, #5636a-5639a

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

Updated August 25th:
Here is the first-day postmark for this issue:The Digital Color Postmark measures 3.0″ x 1.48″. There is no pictorial postmark for this issue.

[ceremony advisory]
Message Monsters Ready to Bring a Smile to Your Mail

WHAT: The U.S. Postal Service will celebrate Message Monsters with the most playful, customizable Forever stamp design ever. The four monster illustrations on this pane of 20 stamps invite interactivity with dozens of self-adhesive accessories on the selvage. The monster-ific accoutrements include cartoony voice balloons and thought bubbles with exclamations and salutations, hats and crowns, hearts, stars, crazy daisies and other fun flair.

Art director Antonio Alcalá designed the pane with original artwork by Elise Gravel, author and illustrator of popular children’s books.

The first-day-of-issue event for the Message Monsters Forever stamp is free and open to the public. News of the stamp is being shared with the hashtag#MessageMonstersStamps.

WHO: Jeffery A. Adams, vice president, corporate communications, U.S. Postal Service

Angie Grau, owner, Paper June Books

Tom Underwood, executive director, NOTO Arts & Entertainment District

WHEN: Friday, Sept. 24, 2021, at 11 a.m. CDT

WHERE: Redbud Park
924 N Kansas Ave
Topeka, KS 66608

RSVP: Dedication ceremony attendees are encouraged to RSVP at: usps.com/messagemonsters.

BACKGROUND: The U.S. Postal Service unleashes the most playful, participatory postage stamps ever — stamps that welcome you to customize a collection of cute and crazy critters. They’ll ride through the mail, adapted by you, adding mirth to your messages.

The 20 Message Monsters on the pane, in four different designs, invite you to enhance your mail with the included adhesive accessories. These little monsters are totally adorn-able. Make them yours and they’re even more delightful!

The stamp designs start with the playful illustrations of Elise Gravel, whose characters are frisky, fresh and full of fun. Colorful characters populating the pane include a roundish, rosy rascal with a sunny tummy; a silly, striped imp waving a four-armed howdy; a squiggly, squid-ly yellow critter with enough eyes to go around; and a reddish rapscallion in short shorts. Whimsical, wacky and inviting your inventiveness, these creatures appeal across generations.

The Message Monster stamp dedication event falls during “Thinking of You Week,” which runs Sept. 20–26. It was first launched in the United Kingdom in 2014 and brought to the United States in 2018 by the Greeting Card Association. What better way to let someone know you’re thinking of them than to send a funny, friendly monster through the mail?

Preorders for the Message Monsters Forever stamps can be made online at usps.com/stamps beginning Aug. 30.

Customers may purchase stamps and other philatelic products through the Postal Store at usps.com/shopstamps, by calling 844-737-7826, by mail through USA Philatelic, or at Post Office locations nationwide.

The Postal Service generally receives no tax dollars for operating expenses and relies on the sale of postage, products and services to fund its operations.

From the Postal Bulletin:
On September 24, 2021, in Topeka, KS, the United States Postal Service® will issue the Message Monsters stamps (Forever® priced at the First-Class Mail® rate) in four designs, in a pressure-sensitive adhesive (PSA) pane of 20 stamps (Item 481300). These stamps will go on sale nationwide September 24, 2021, and must not be sold or canceled before the first-day-of-issue. The Message Monsters pane of 20 stamps may not be split and the stamps may not be sold individually.

The four designs on this new pane of 20 stamps invite interactivity with dozens of self-adhesive accessories that personalize these comical characters for delighted recipients. Decorations include hearts, hats, voice balloons, flowers, and thought bubbles. Art director Antonio Alcalá designed the pane with new illustrations by Elise Gravel.

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 – Message Monsters Stamps
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 January 24, 2022.

Technical Specifications:

Issue: Message Monsters Stamps
Item Number: 481300
Denomination & Type of Issue: First-Class Mail Forever
Format: Pane of 20 (4 designs)
Series: N/A
Issue Date & City: September 24, 2021, Topeka, KS 66603
Art Director: Antonio Alcalá, Alexandria, VA
Designer: Antonio Alcalá, Alexandria, VA
Artist: Elise Gravel, Montreal, Quebec
Modeler: Sandra Lane/Michelle Finn
Manufacturing Process: Offset
Printer: Banknote Corporation of America
Press Type: Gallus RCS
Stamps per Pane: 20
Print Quantity: 18,000,000 stamps
Paper Type: Phosphor, Block Tag
Adhesive Type: Pressure-sensitive
Colors: Black, Cyan, Magenta, Yellow
Stamp Orientation: Vertical
Image Area (w x h): 1.085 x 1.42 in./ 27.559 x 36.068 mm
Overall Size (w x h): 1.225 x 1.56 in./31.115 x 39.624 mm
Full Pane Size (w x h): 7.75 x 8.19 in./196.85 x 208.026 mm
Press Sheets Size (w x h): 14.5 x 18.25 in./368.3 x 463.55 mm
Plate Size: 60 stamps per revolution
Plate Number: “B” followed by four (4) single digits in two corners
Marginal Markings:
Front: Header: Message Monsters • Plate number in bottom two corners
Back: ©2020 USPS • USPS logo • 2 barcodes (481300) • Plate position diagram (3) • Promotional text