Signals Page Reference Accumulator

    Enter the signal name, followed by the page numbers
    on which entries or exits occur (each page reference
    is logged immediately after the delimiting space is
    typed), followed by a zero to end the list (causing
    output of a carrige-return).

    During input, if a previously entered signal-list
    needs modification, enter its name (which will dis-
    play the current list), followed by the additional
    page numbers and zero.

    Should any page reference need deleting from a given
    signal list, enter the signal-name (which displays
    its page references) followed by negative-page-number
    then zero.  Deleting all page references will result
    in the removal of the signal-label entry entirely.

    A null entry for a label-name ends input session and
    prints lists (found in the global variable
    *signal-labels*).