In an online experiment, we measure users' interactions with search engines, both in standard configurations and in modified versions with improved labels identifying search engine advertisements. In particular, for a random subset of users, we change "sponsored link" labels to instead read "paid advertisement." We find that users receiving the "paid advertisement" label click 25% to 33% fewer advertisements and correctly report that they click fewer advertisements, controlling for the number of advertisements they actually click. Results are most pronounced for commercial searches, and for users with low income, low education, and little online experience.