A communication system includes: at least one user terminal; a printer; a storage device; a registering unit; and a list transmitting unit. The printer includes a print controlling unit that prints an image on a recording sheet based on target print data received from a user terminal, and that prints on the same recording sheet a mark set by the user terminal according to a mark configuration parameter. The registering unit records in the storage device a combination of a mark configuration parameter and identification data that is received from one of the at least one user terminal, the mark configuration parameter indicating configuration of a mark that has been set at the subject user terminal, the identification data identifying one user that has set the mark. The list transmitting unit transmits to each user terminal data of a mark list that lists up at least one combination of the mark configuration parameter and the identification data that has been stored in the storage device.