Many Android apps contain advertising modules provided by third parties in order to monetize their development efforts. Airpush is a company that produces one of the more aggressive advertising modules. Their advertising modules can place ads in the Android notification bar where users are alerted to events such as missed messages or missed phone calls.
Source: http://www.symantec.com/connect/blogs/airpush-begins-obfuscating-ad-modules Costin Ionescu