Q: Why does my machine show a Test Mode stamp in the bottom right corner of my desktop?

A. If your system shows a "Test Mode" stamp in the bottom right corner of your display you have likely turned on test signing of drivers.

This can be confirmed with the bcdedit /enum command (note the testsigning value):

C:\Windows\system32>bcdedit /enum
Windows Boot Manager
--------------------
identifier {bootmgr}
device partition=\Device\HarddiskVolume7
description Windows Boot Manager
locale en-US
inherit {globalsettings}
bootshutdowndisabled Yes
default {current}
resumeobject {5f599037-de4a-11e1-8931-b2ebfcc6f15f}
displayorder {current}
toolsdisplayorder {memdiag}
timeout 30

Windows Boot Loader
-------------------
identifier {current}
device partition=C:
path \Windows\system32\winload.exe
description Windows Server 2012
locale en-US
inherit {bootloadersettings}
recoverysequence {5f59903b-de4a-11e1-8931-b2ebfcc6f15f}
recoveryenabled Yes
testsigning Yes
allowedinmemorysettings 0x15000075
osdevice partition=C:
systemroot \Windows
resumeobject {5f599037-de4a-11e1-8931-b2ebfcc6f15f}
nx OptOut

To fix the problem turn off the test signing and enable the integrity checks:

C:\Windows\system32>bcdedit.exe -set loadoptions ENABLE_INTEGRITY_CHECKS
The operation completed successfully.

C:\Windows\system32>bcdedit.exe -set TESTSIGNING OFF
The operation completed successfully.