On a bus today I didn't have enough money on my oyster card (£1.10 - so 10p short of a journey) so i slipped a fiver onto the cash tray and they guy couldn't find any change so he issued me with an 'unpaid fair notice' and filled it in....he told me to do something, but i didn't hear him properly and he started driving so I couldn't ask what he said.

Are these just a free journey ticket if the bus company can't give you change?

Also, do they have a limit on the number of these they can give a day?

You can also get these if there is a problem with the machine or you look vulnerable or in distress (it says this on the back of the ticket)