Material Design – Android Application – How to indicate the existence of unsynchronized data

I have an Android application where users can create different types of content on different screens of the application. All content is synchronized with the server in a background thread. Normally this happens instantly, when new data is created, but if the device is offline, unsynchronized content may exist for a longer time.

For the user to realize that (so that he does not ask when comparing the content of the application and the content of the server through the web interface), I thought about showing an indicator somewhere in the application.

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

Ideas so far

  • Show the indicator as a lot type in the navigation drawer symbol ("burger" icon) but that would become quite small.
  • Use a notification, but since the indicator will disappear on its own, as soon as the synchronization is done, that seems a kind of abuse of the idea of ‚Äč‚Äčnotification.
  • It shows a colored line at the top or bottom of the action bar, but that does not explain itself.