(Red triangle)Device is corrupt after flashing Android N Dev Preview on rooted Nexus 6P Just got my brand new Nexus 6P about a week ago (Yeah, stupid me). I immediately began to root my device using this thread on XDA:
http://forum.xda-developers.com/nexus-6p/general/guides-how-to-guides-beginners-t3206928

What I've done along following the guide:


Unlocked the bootloader using fastboot;
Installed TWRP custom recovery using fastboot;
Rooted my device by flashing the stable version of SuperSU through the custom recovery just installed.


This process went flawless. Booted up my device, noticed no bugs/weird problems at all.

As I watched some Android N Dev Preview videos, I decided to flash it myself. Now, my experience in flashing images on android is not low as I've done it a couple times before. The installation seemed flawless, as I followed these steps in order (yes, my bootloader is unlocked):


flashed the bootloader.img
flashed the radio.img
flashed the recovery.img
flashed the boot.img
flashed the system.img
rebooted bootloader after each step


When I booted my devices, It displayed an message saying something like: couldn't verify if device is corrupted. I've seen this before, and I know this occurs when the bootloader is unlocked, so I waited 10 seconds till another similar message occurred:


  /!\
  Your device is corrupt. It can't be trusted and may not work properly.
  
  Visit this link on another device:
  g.co/ABH


I haven't seen this before so I looked it up and realized my device is bricked.

What I have done so far after the message


Carefully applied the steps again in the same order;
Carefully applied the steps again but with recovery and boot swapped;
Factory reset (result is very obvious I know);
Waited for a long, long time


What is, in my situation, your advise for me to at least unbrick the device? I've downloaded the latest version of Marshmallow on the Google Factory Images for Nexus devices page. Should I just flash this image?

Please remind that I'm rooted.

Many thanks!
There is nothing to worry about. It means you just flashed a ROM.

More details: https://support.google.com/nexus/answer/6185381?hl=en