Reference: Telegard's ACS System

Here's what Telegard originally did, it's pretty reasonable.
This is also close to what MysticBBS uses.

                  Telegard Bulletin Board Software, v3.10
                       REFERENCE: Security ACS Codes

                      Copyright (C) 1998 by Tim Strike
                            All Rights Reserved.


    The following ACS functions are available for Telegard 3.10.

    ACS   Parameters   Description                          Example
    ---   ----------   -----------------------------------  ----------
    #C    "text"       "text" in User.Comment field         #C"CBV"
    A     <n>          User of age >= <n>                   A18
    B     <n>          Connection rate >= <n> (baudrate     B144
                           minus the last two zeros)
    C     <c>          Current group 1 = <c>                CT
    D     <c>          Current group 2 = <c>                DF
    E     <c>          User with flag 1 <c>                 EA
    F     <c>          User with flag 2 <c>                 FA
    G     <c>          User gender = <c>                    GF
    H     <n>          Hour of day = <n>                    H10
    I     <s>          User ID = <s,form: nnnn)             I0001, I00RA
    J     <n>          Message board = <n>                  J0
    K     <n>          File board = <n>                     K1
                       (above two functions use raw message
                           area numbers - i.e. the numbers
                           before area compression)
    L     <n>          User total calls >= <n>              L14
    M     <n>          User public posts >= <n>             M50
    N     <n>          Node number = <n>                    N1
    O     <n>          Online time >= <n>                   O15
    P     <n>          User filepoints >= <n>               P25
    R     <c>          User with restriction <c>            RE

                         L - Logon only ONLY per/day
                         C - Can't page SysOp
                         A - Can't post AutoMessage
                         * - Can't post anonymous
                         E - Can't post private
                         N - Can't post Netmail
                         P - Can't post at all
                         K - Can't vote
                         M - Forced mail deletion
                         G - Can't post Echomail
                         1 - No UL/DL Ratio
                         2 - No post/call Ratio
                         3 - No File Point Check
                         4 - Protection from Deletion
                         5 - No Daily DL Ratio
                         6 - No DL Time Check
                         7 - No Forced PW Change
                         8 - Time Per Call 

    S     <n>          User security level >= <n>           S25
    T     <n>          User timeleft >= <n>                 T40
    V     <c>          User ratio test

                         K - User passed UL/DL K ratio
                         P - User passed post/call ratio
                         T - User passed post/time ratio
                         U - User passed UL/DL ratio

    W     <n>          Day of week = <n>                    W0
                          0=Sunday..6=Saturday
    X     <c>          Misc User Testing                    XA|XV

                         A - User has ansi graphics
                         I - User has full-line input ON
                         C - SysOp is available
                         E - Error Correcting connection
                         F - FileSysOpACS (current area)
                         L - Local logons
                         M - MessageSysOpACS (current area)
                         N - User in newuser process
                         P - User has pause ON
                         Q - Files are queued for download
                         R - User has RIP graphics
                         S - User has SysOpACS
                         T - User has TTY graphics
                         V - User has Avatar graphics
                         X - User is in expert mode
                         Z - User has CoSysOpACS
        
    Y     <n>          Minutes of current day >= <n>        Y60
    Z     <c>          User subscription level = <c>        ZB
                       (Note: the user subscription level is
                        updated if user sl/flag changes are
                        done through the subscription system
                        (auto/manual); changing them separately
                        does not update the subscription level)

    &                  AND                                  S25&FA
    |                  OR                                   C@|CA
    !                  NOT                                  S25&!S50
    ()                 Grouped ACS                          (S5&!S10)|VP
    ^                  TRUE                                 ^
    %                  FALSE                                %