What is this in my system tray? Every so often, seemingly random, this notification appears in my notification bar, but not in the tray.



The circles on the left in the notification bar. I have no clue what it's related to. There's no notification if I slide the tray down. It doesn't stay long, about the time I check for it in the notification tray, it's gone. I develop for my phone. Would anything on the development side of things trigger this weird notification?

It's a Samsung Galaxy S3 running CyanogenMod nightlies, specifically 10.1-20130405-NIGHTLY-d2spr which is Android 4.2.2.

EDIT:

I've noticed that this appears very consistently when I have Moon+ Reader open. It does not appear to be a notification caused by that app, but instead appears to be that the app is somehow "muting" notifications that happen while it is open. Is there something in the API that allows for the silencing of notifications originating from other apps?
I've found it in the Android API: http://developer.android.com/reference/android/view/View.html#setSystemUiVisibility(int)

A flag, SYSTEM_UI_FLAG_LOW_PROFILE, can be passed to indicate that certain UI elements be put into a Low Profile and offer less of a distraction to the user. If I had a nexus device (really any device with soft buttons across the bottom) then I would also notice those buttons being replaces by the same dim circle I'm seeing in my navbar.

This has been available since 4.0 and is intended for book readers, games, and other immersive applications.