This tutorial from Sourabh Soni explains how to implement hashtags in Android applications using the Linkify class in the Android SDK, and in a more general sense, how to make any text work as a hypertext link. Hashtags are pretty commonplace these days, and their implementation in Android is not immediately apparent at all, so Soni's tutorial is a welcome resource for any Android developer looking for some extra organizational capabilities.
Soni's tutorial is particularly thorough, too. He walks you through the entire process, and all the code for a complete example app that implements hash tags is there for you - you can download the whole thing on GitHub. And even if you're not interested in hashtags in particular, there is a lot of useful information here on the Linkify class which, according to Soni, is a particularly diverse and useful class that can go a long way toward improving user experience.
Check out the full tutorial to get your hashtags working.