Windows 7, like Windows Vista has several watermarks which appear when certain situations warrant it so. One of them is the Test Mode watermark.
This watermark may appear in the bottom right part of your Windows desktop, if you install an application whose drivers are not digitally signed
by Microsoft and if they are still in the testing phase.

Most are familiar with For testing purposes only, Evaluation copy, Safe Mode, etc watermarks. The Test Mode is not so familiar a watermark, however!

The TESTSIGNING boot configuration option determines whether Windows 7 or Vista will load any type of test-signed kernel-mode code. This option is not
set by default, which means test-signed kernel-mode drivers will not load by default on 64-bit versions of Windows Vista and later versions of Windows.

For 64-bit versions of Windows 7 & Vista the kernel-mode code signing policy requires that all kernel-mode code have a digital signature. However,
in most cases, an unsigned driver can be installed and loaded on 32-bit versions of Windows Vista and later versions of Windows, explains MSDN.

The TESTSIGNING boot configuration option is enabled or disabled through the BCDEdit command.

To enable test-signing, use the following BCDEdit command:

Bcdedit.exe -set TESTSIGNING ON

or

runas /user:administrator "Bcdedit.exe -set TESTSIGNING ON"

To disable test-signing, use the following BCDEdit command:

Bcdedit.exe -set TESTSIGNING OFF

or

runas /user:administrator "Bcdedit.exe -set TESTSIGNING OFF"