Please make an effort to bring your DCI number to a tournament.  While it is possible to looks up players’ numbers on site, the tournament can get started much easier and quicker if staff does not have to look up a lot of DCI numbers.  One recommended trick is to enter your DCI number into your phone as a contact.  If you have not played in sanctioned DCI tournament before, you can get a DCI number when registering at your first event.