On most of the devices we maintain there are white labels with the names of the computer printed on them.
The label will look something like the image below.
Please Note: Your school may be prefixed differently.
If you are unable to locate this sticker or it has been removed then follow on below:
1- Log out of the computer
2- On the log on screen there will be an option to click underneath the two log on bars for username and password. It will say "How do I sign into another domain"
if you click this the name will be prefixed by a "\".