What is this notification icon that looks like a raindrop? My friend bought a Sony Xperia Z3, and started to install all the apps she liked. After installing dozens of apps, she realized that there is a notification icon looks like a raindrop. I was asked to get rid of it, but I couldn’t. I tried to stop all the running apps, but it remained on top. If she pulls down the notification bar, it shows nothing. 

Any idea what this could be?status
I would start by looking at the list of currently running apps in Settings -> Apps  -> Running (could be different on Sony's devices.)

Narrow the list down by ignoring Google's and Sony's own services (e.g. Google Play serviced, Google Search, Google Keyboard, etc.)  Now examine each app that you don't recognize by taping on it, and tapping the "Stop" button.  If the icon on top disappears - that's the app which was spawning it.  You should now be able to open the app, go into its settings and look for a way to disable the notification icon.

If you are still unable to find the app after going through all 3rd-party apps, it's probably one of the system apps belonging to Sony.