VMS Help DCL Tips, UIC  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    A UIC is a user identification code that can be in either numeric
    or named format. When a DCL command requires a UIC specification,
    you can specify either format. However, the system converts all
    UICs to numeric format when determining a user's access to a data
    resource.

    A UIC in numeric format consists of a group number and a member
    number in the format:

       [group,member]

    where:

    group  is an octal number in the range 0 through 37776
           representing the group number.
    member is an octal number in the range 0 through 37776
           representing the member number.

    The square brackets are required in the UIC specification. You
    can also omit leading zeros when specifying group and member
    numbers.

    A UIC in named format consists of a member identifier and
    optionally, a group identifier, as shown in either of the
    following:

       [member]

       [group,member]

    The group and member identifiers can each contain up to 31
    alphanumeric characters and must contain at least one alphabetic
    character. The names can include the characters A through Z,
    dollar signs ($) underscores (_), and the numbers 0 through 9.
    The brackets are required in the UIC specification.

    The member number is unique for each user on the system, and is
    equivalent to the user's numeric UIC (including both the group
    and the member numbers). The group identifier is equivalent to
    only the group portion of the UIC.

    For additional information on specifying UICs, refer to the
    OpenVMS Guide to System Security.