The actual empty car indicator used to be a lighting type or a Maku type (a type in which displayed items are switched by changing written cards or panels), but majority of the current indicators are LED type, which can indicate 'SOS' or 'HELP' in an emergency by linking with the company name indicating lamp.
以前は電照式や幕式が多かったが、最近は発光ダイオード表示タイプの物が多く、緊急時に社名表示灯と連動して「SOS」や「助けて」と表示するものもある。