The "tag" command:

Usage: fossil tag SUBCOMMAND ...

Run various subcommands to control tags and properties.

    fossil tag add ?OPTIONS? TAGNAME CHECK-IN ?VALUE?

        Add a new tag or property to CHECK-IN. The tag will
        be usable instead of a CHECK-IN in commands such as
        update and merge.  If the --propagate flag is present,
        the tag value propagates to all descendants of CHECK-IN

        Options:
          --raw                       Raw tag name.
          --propagate                 Propagating tag.
          --date-override DATETIME    Set date and time added.
          --user-override USER        Name USER when adding the tag.
          --dryrun|-n                 Display the tag text, but do not
                                      actually insert it into the database.

        The --date-override and --user-override options support
        importing history from other SCM systems. DATETIME has
        the form 'YYYY-MMM-DD HH:MM:SS'.

    fossil tag cancel ?--raw? TAGNAME CHECK-IN

        Remove the tag TAGNAME from CHECK-IN, and also remove
        the propagation of the tag to any descendants.  Use the
        the --dryrun or -n options to see what would have happened.

    fossil tag find ?OPTIONS? TAGNAME

        List all objects that use TAGNAME.  TYPE can be "ci" for
        check-ins or "e" for events. The limit option limits the number
        of results to the given value.

        Options:
          --raw           Raw tag name.
          -t|--type TYPE  One of "ci", or "e".
          -n|--limit N    Limit to N results.

    fossil tag list|ls ?--raw? ?CHECK-IN?

        List all tags, or if CHECK-IN is supplied, list
        all tags and their values for CHECK-IN.

The option --raw allows the manipulation of all types of tags
used for various internal purposes in fossil. It also shows
"cancel" tags for the "find" and "list" subcommands. You should
not use this option to make changes unless you are sure what
you are doing.

If you need to use a tagname that might be confused with
a hexadecimal baseline or artifact ID, you can explicitly
disambiguate it by prefixing it with "tag:". For instance:

  fossil update decaf

will be taken as an artifact or baseline ID and fossil will
probably complain that no such revision was found. However

  fossil update tag:decaf

will assume that "decaf" is a tag/branch name.