In any park where you are making a lot of money, or in a sandbox park, go to the research tab of the park overview menu and select three TV ads (these cost 5000 each).
It won't pop right away, you have to let it run for a while, so exit the menu and then speed up time and let the park run until the ad campaigns have completed a run. After they are done, the trophy should pop. If not, try cancelling one of the ad campaigns, that might help!