The letters on a scratch off lottery ticket indicate the amount of money that person has won. According to Wild104fm.com, the letters are abbreviations for the winning prize amounts on the ticket.
If there is an "X" on the ticket, that means the ticket is not a winner. Most lottery tickets show the winning amount and have that number written out as well. For example, if a person won $50, the lottery ticket would write out both "50" and "fifty". The letters do not necessarily need to be abbreviated in order to be written on the ticket; however, words are sometimes abbreviated for space.