Do you have to have a block around the postage paid permit stamp?

According to examples provided by the United States Postal Service, the acceptable alternative to the square block border around a postage paid permit stamp is a circular border. Individuals may inquire about further altering a permit imprint indicia by contacting a mail-piece design analyst.

In order to be accepted by the United States Postal Service, a design for a permit indicia must include a class marking on line one. Line two must include the words "U.S. Postage Paid." Line three is for the city and state from where the permit is issued. The word "permit," along with the permit number, appears on the fourth line of the stamp.