Passenger car side indicator lamp

[al camino]

Hi to all

 

I tried some search here in Forum but failed.

 

Lot of my passenger roling stock has red indicator lamps on the car side.

Which function is behind these lamps?

Does it help testing the brakes or indicate the car is occupied?

 

May I kindly ask which term would have made my search successful?

 

[katoftw]

Doors closing