"A notice is a public pronouncement by the Service that may contain guidance that involves substantive interpretations of the Internal Revenue Code or other provisions of the law." (Notice Defined, IRM § 220.127.116.11.3)
"Notices are public announcements issued by the Internal Revenue Service. Notices appear in the Internal Revenue Bulletin and are included in the bound Cumulative Bulletin." (Miscellaneous Documents, IRM § 18.104.22.168.4.1)
"IRS Notices are public pronouncements containing guidance that involves substantive interpretations of the code or other provisions of the law. Notices may also be used for materials that would be appropriate for an announcement, but otherwise need to be preserved in the Cumulative Bulletin. . . ." (Inventory of IRS Guidance Documents — A Draft, Tax Notes Today)
The following citation resources may be informative.
Below are links to select sources offering notices.