Add an enclosure notation after your signature at the end of the letter, and abbreviate it with "Enc." or "Encl. In this article, we detail when to use a formal letter format, the different types of formal letters and how to write your own.In this article, we explain what an enclosure is and how to cite one, and we provide an example of an enclosure in a business letter. 13. Enclosures. An enclosure can prevent a letter from becoming too detailed. Guidance documents include memoranda, statements of policy, interpretive rules, staff manuals, circulars, bulletins, advisories, or frequently asked questions. Compliance with disclosure and notification regulations. The enclosure letter should be designed to serve those persons as well. The Self Study Assessment Review Readiness Packet, as prescribed in reference (d), is no longer a requirement, but it can be used as a template. Additional letter designations with (W) or (OW) are preferred but not required. 5. Please see Illustration below for instructions 2, 3, and 4.