This paper explores how developers using AI code generation tools self-declare their AI-generated code and why. Through analysis of GitHub repositories (collecting 613 AI-generated code snippets) and a survey (111 valid responses), we found that 76.6% of developers always or sometimes self-declare their AI-generated code, while 23.4% never do so. Reasons for self-declaring included tracking and monitoring for future review and debugging, as well as ethical considerations. Reasons for not declaring included extensive modifications to the AI-generated code and the perception that it would be unnecessary. Finally, we provide guidelines for self-declaring AI-generated code to address ethical and code quality concerns.