kernel - How can I check if a device is booted into safe mode from adb?

Is it possible to use adb to detect whether a device is booted into "Safe Mode" or normal mode?

I've looked through the output of getprop and other command-line tools and haven't found any good indicator of safe mode, at least not on my N5/hammerhead device.

Update: I'm trying to check whether or not the device is in Safe Mode, not to force it into Safe Mode. Putting the device in Safe Mode programmatically is relatively straightforward and well-documented.

Any ideas?