This is a text string reporting the state of the EIA electrical signal levels for this port, interpreted according to that port's specific DIM type and DTE/DCE configuration. An admin uses it to diagnose serial-line connectivity problems, since a given signal-level reading only makes sense once you know the installed DIM type and its configuration. As an illustrative example, the string might read "Signal OK" when the expected leads are asserted, or report a fault if a required signal such as DCD is missing.