Android 6.0 Marshmallow's Demo Mode cleans up the statusbar, so developers can take cleaner screenshots.
This app adds a QuickToggle in CyanogenMod 13's pull down actions to toggle the Demo Mode.
You can toggle the Demo Mode from the QuickToggle, or from the main app screen.
There is also a launcher widget from which you can toggle the Demo Mode.
Root Access is needed to force Demo Mode on the system.