The effectiveness of an organization's security awareness program can be measured by capturing data on changes in the way people react to threats, such as the ability to recognize and avoid social engineering attacks1. An increase in the number of phishing emails reported by employees indicates that they are more aware of the signs and risks of phishing, and are more likely to take appropriate actions to prevent or mitigate the impact of such attacks23.
References
1: The Importance Of Measuring Security Awareness 2: Measuring the effectiveness of your security awareness program 3: How effective is security awareness training?