Android App – How to indicate existence of unsynchronized data

I have an Android application where the users can create different kinds of content in different screens of the app. All content is synced to the server in a background thread. Normally this happens instantly, when new data is created, but if the device is offline, unsynced content can exist for a longer time.

To make the user aware of that (so he doesn't wonder when comparing app's content and server's content via web interface), I thought of showing an indicator somewhere in the app.

I am not sure, how/where I should show such an indicator. I cannot show the indicator in the action bar, because it is used for different things in many screens.

Ideas so far

• Show indicator as a kind of a batch on the navigation drawer symbol ("hamburger" icon) but that would become quite small.
• Use a notification, but as the indicator will go away by itself, as soon as synchronization is done, that seems as kind of an abuse of the notification idea.
• Show colored line at the top or bottom of the action bar, but that isn't self explanatory.