  Online political advertising has grown significantly over the last few years.
To monitor online sponsored political discourse, companies such as Facebook,
Google, and Twitter have created public Ad Libraries collecting the political
ads that run on their platforms. Currently, both policymakers and platforms are
debating further restrictions on political advertising to deter misuses.
  This paper investigates whether we can reliably distinguish political ads
from non-political ads. We take an empirical approach to analyze what kind of
ads are deemed political by ordinary people and what kind of ads lead to
disagreement. Our results show a significant disagreement between what ad
platforms, ordinary people, and advertisers consider political and suggest that
this disagreement mainly comes from diverging opinions on which ads address
social issues. Overall our results imply that it is important to consider
social issue ads as political, but they also complicate political advertising
regulations.
