Q:

What do you call a notepad used to keep a record?

Let's say we're in a computer room of an university. In order to use a computer, you have to write your name, department, and seat number in a notepad.
What do you call that notepad? Or what adjective should you use to describe it?

A:

It's a log book or simply, log.

A log book is a book in which someone records details and events relating to something, for example a journey or period of their life, or a vehicle.

In corporate buildings, I always see log books near the security area/concierge so they can record the names of the visitors who come in and out of the building, and the time they went in and out as well, for security purposes.
This may be used in other similar situations where tracking of activities is important. i.e., in your question, the usage of computers in a university computer room.

A:

A register or guest register. 'an official list or record' 

A:

At my university, "sign in sheet". If you search for "sign in sheet" you can find many examples of similar sheets for various situations.

