markers occasionally as follows:
When a player buys in for, say, £1000 or £2500 with a 'sealed packet' of notes, a 'suit' will check to make sure the packet has not been tampered with and if satisfied, rather than opening and counting (the packet is too thick to go in the drop slot) they will place such a marker on the wheel to indicate they have removed the packet and taken it directly to the cage. At the cage it will be swapped for a plaque. The suit brings the plaque back to the table where it is dropped and the marker returned to its allocated place. I guess this is for the benefit of the cameras.