The Range Safety Armed light was a cue for the crew to eject during the Orbital Test Flight period of the Shuttle program. After the ejection seats were removed from Columbia, the light was still there.
See Space Shuttle Range Safety System in the Rogers Commission Report.
The location of the indicator changed after the Orbiter 'glass cockpit' upgrade, but it was in the vehicles until the end of the program.
(Personal photo taken in Orbiter cockpit in May 2008, drawing from SCOM, see link below)
For the latter part of the program, the only Range Safety System left on the stack was in the Solid Rocket Boosters. So if Range Safety actions had to be taken in 2nd stage, the illumination of this light served as a backup or no-voice-comm cue to the crew to take the actions they had been briefed on.
During first-stage, trajectory deviations may lead to a violation of a
destruct line by a shuttle that is still under control. It may be
possible to return the vehicle toward its nominal trajectory or to
safely execute an abort. Therefore, the Flight Director (FD) and
Flight Dynamics Officer (FDO) are in voice communication with the
Flight Control Officer (FCO) (formerly Range Safety Officer) during
ascent. If the FCO detects a violation, the FDO and FD are immediately
informed. The FD must determine whether the shuttle is controllable or
uncontrollable, and inform the FCO. As long as the FD declares the
shuttle controllable, the FCO takes no action to terminate the flight
for trajectory deviations alone.
Range Safety Limit Avoidance
A deviation from nominal trajectory that is large enough to warrant
FCO action must be corrected. First-stage options are:
• State vector
• Select CSS (after 90 seconds MET)
• Engage BFS
In second stage, the options are:
• State vector update
• ATO selection
• Select CSS
• TAL or RTLS
• Engage BFS
• SSME manual cutoff. For loss of comm, FCO
will send the ARM command as a cue for manual MECO
Options are listed in order of priority. The priorities are
established such that higher priority options preserve lower priority
options and involve fewer new dangers to the crew and shuttle when
Source: Shuttle Crew Operations Manual, page 6.2-5 (emphasis mine)