This is a portion of a Panel Sender Alarm, Prime and make busy panel. As can be seen in the photo Sender Frame 303 'SDR303' has Sender 'C' in alarm or 'stuck'. To try to release the stuck sender the button above the lamp would be pulled out and pushed back in. If this did not release the sender manual action was required at the sender itself. Also in this photo you will note Sender frame 304 'SDR304' has a maintenance tag for sender 'J'. Also note that there is no sender 'I'.