Mercury spacecraft control panel status indicator shell, labeled “O2 EMER”
for oxygen emergency.
Consists of an aluminum shell mounting a translucent plastic window
with engraved label. Two lights mounted on the panel behind the indicator window would illuminate amber when emergency oxygen flow to the suit was activated.
Appears to be identical to the flight indicator design.
Photo of Friendship 7 control panel shows column of status indicators, with this type of indicator third from the top.