As digital platforms become a key channel for political advertising, there are continued calls for expanding regulation of digital political ads as a distinct content category. However, designing policies to meet these demands requires us first to decipher what the public perceives a “political” ad to be. In this article, we report two preregistered experiments to understand factors that drive public perceptions of what makes an ad political. We find that both advertiser-level cues and content-level cues play an independent role in shaping perceptions. To a lesser extent, participants also attribute political meaning to ads that clash with their own preferences. These patterns were replicated in a conjoint study using artificial ads and in an experiment using real-world ads drawn from the Facebook Ad Library. Our findings serve as an important benchmark for evaluating proposed definitions of political ads from policymakers and platforms.