Locating Your Serial Number
Use any of these methods to find your Mac Pro serial number:
Choose Apple () from the menu bar and then choose About This Mac. Click the
version number beneath the words “Mac OS X” to cycle through the Mac OS X version
number, the build version, and the serial number.
Open System Information in the Utilities folder in Launchpad and click Hardware.
Look on the configuration label, which is located on the back of your Mac Pro near
the video ports.