Regulators have extensively used warning signs in many health domains to enhance knowledge and shift attitudes and behaviors to reduce associated harm. The effectiveness of these signs is influenced by their physical attributes and content. Gambling warning signs traditionally focus on the following: informing individuals of the potentially risky outcomes of gambling and the odds of winning, encouraging gambling within affordable limits, and advertising counseling services. The limited evidence suggests that warning signs for gambling attract attention and improve knowledge but are generally ineffective in modifying players' thoughts and behaviors. Therefore, the authors aimed to determine the optimal content of messages that would enhance responsible gambling practices. The authors conclude that, in contrast with signs displaying probabilities or informing players of the risks associated with gambling, signs designed to encourage players to reflect on, appraise, evaluate, and self-regulate their actions have greater theoretical and empirical support. The authors comment that warning signs should promote the application of self-appraisal and self-regulation skills rather than the simple provision of information on odds and probabilities to maximize their effectiveness as a public health tool.