In the UK, public transport buses used to be staffed by a team of two: the driver and the conductor. The conductor's job was to walk around the bus, selling tickets to new passengers and generally assisting them - ringing the bell for them, telling them when they need to get off, and suchlike. In my youth, they would dispense tickets from a crank-handle operated machine slung around their waist. Nowadays, tickets are either bought from the driver or from some kind of machine as you get on the bus, and the role of bus conductor has become extinct.