Electronic gaming machines are popular among problem gamblers; in response, governments have introduced "responsible gaming" legislation incorporating the mandatory display of warning signs on or near electronic gaming machines. These signs are designed to correct irrational and erroneous beliefs through the provision of accurate information on probabilities of winning and the concept of randomness. There is minimal empirical data evaluating the effectiveness of such signs. In this study, 93 undergraduate students were randomly allocated to standard and informative messages displayed on an electronic gaming machine during play in a laboratory setting. Results revealed that a majority of participants incorrectly estimated gambling odds and reported irrational gambling-related cognitions prior to play. In addition, there were no significant between-group differences, and few participants recalled the content of messages or modified their gambling-related cognitions. Signs placed on electronic gaming machines may not modify irrational beliefs or alter gambling behaviour.