The "tag" command:

Usage: fossil tag SUBCOMMAND ...

Run various subcommands to control tags and properties

    fossil tag add ?--raw? ?--propagate? 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 propages to all descendants of CHECK-IN

    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.

    fossil tag find ?--raw? ?--type TYPE? TAGNAME

        List all objects that use TAGNAME.  TYPE can be "ci" for
        checkins or "e" for events.

    fossil tag list ?--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.

only allow --date-override and --user-override in 
  fossil tag add --date-override 'YYYY-MMM-DD HH:MM:SS' \
                  --user-override user 
in order to import history from other scm systems