An Indicia is a convenient way to pay for postage when you send bulk mail. This means you don’t have to run the mail through a meter, or buy stamps and affix them to each piece of mail. Anyone can apply online for a permit. There is an annual fee you must pay to use the indicia.
It can also be a printed logo or piece of artwork in the top right hand corner of a mailed envelope that indicates postage has been paid by the mailer. Indicia is used on envelopes included in direct mail that includes response forms, as a way to encourage and simplify reader response.
The post office has specific rules for the types of mail it can be used on, what an indicia says, and where it is placed on the mail piece.