A ticket prefix puts one to four characters in front of every ticket number a device generates, so you can tell at a glance which terminal opened a ticket.
A device with prefix A generates ticket numbers such as A12, A13, A14.
Match the prefix to the station name: B for bar, P for patio, S1 and S2 for server stations, H1 for the first handheld. Write the scheme down somewhere the site can find it, because the next person to add a terminal will need it.
Source: Global Payments Genius POS User Guide. Newly built article, pending review.