This policy also applies to mobile apps that use Google's AdMob service to serve ads, which tracks users via a device identifier. If your mobile apps use AdMob to serve ads, you'll need a prompt that says so when the app is used for the first time. The prompt should tell users where to find more information about the usage of device identifiers. This applies to any app using AdMob, regardless of whether it's available for Android or iOS.
A bit of history
Google's EU user consent policy (referenced by the AdSense policy) requires publishers to comply with the law. The law we're referring to in the UK is The Privacy and Electronic Communications (EC Directive) Regulations 2003, part of which is derived from European Directive 2002/58/EC, also known as "the e-privacy Directive".
There's a great infographic and some more history about the EU privacy directive on the silktide website.
What to do
Although Google's site gives some guidance, it's still not 100% clear how publishers should meet with the EU requirements, especially related to apps. To comply with Google's policy updates, publishers should fully meet the requirements by September 2015, so hopefully by then we'll have a better idea of exactly what's required based on what other publishers have done.
If you fail to meet these requirements after the deadline, it's not clear exactly what will happen. Google recommends seeking legal advice on how to meet the requirements, although they also acknowledge that it might not be possible for some publishers to do so.
We can help you to implement cookie prompts on existing mobile apps and websites. Contact us now with information about your site or app to have a chat with one of our development experts.