Student wants me to sign a paper to add him or her to my class. What do I do?

You can direct the student to sign up for your class via the portal. Also, Business Advising can help them.

If you happen to know that your prospective student is an Open University student, their ability to join your class is at your discretion and must take into consideration the seats available in your room. We are required to adhere to Fire Marshall rules on capacity of the rooms--more on that below. 

Here is a special note from Mike Rehg that applies to this semester's situation:

Just wanted to make sure everyone knows what the max number of students are in your classrooms. There is no pressure to take on any more students this fall. We are over our goal, and I think even with drops over the next two weeks we should be fine. But if you have room and you want to add a student, that is up to you.
Most importantly, you can't take on students over the capacity of the room even if there are extra chairs. I have listed the Glenn rooms that we use below with the max allowable enrollment.
I believe students can go to advising and get on the waitlist for a class, if there is one. Normally advising sends out a message in that regard, but I haven't seen one this Fall. If a spot opens up in a section then the waitlist will be processed automatically, as far as I know, unless the capacity has been dropped to prevent that from happening.
Let me know if you have any questions -
Glenn 112-62
Glenn 125-47
Glenn 202-40
Glenn 210-34
Glenn 214-50
Glenn 302-40
Glenn 308-36
Glenn 306-50