Okay, I don't want to get too much into all of the legal stuff here, but basically, when a student turns 18 they become their own guardian unless parents do something about it (ex. power of attorney or guardianship).
But sometimes, parents haven't been able to complete that process, and we still want them involved and making decisions in the IEP process. The student has to delegate his/her rights to the parents in order for this to happen. There is specific paperwork (3457K - Delegation of Rights) that needs to be completed, and it is our responsibility, as case managers, to ensure that the student understands what he/she is signing.
I typed up a quick explanation for my students using a symbol-generating word processor (Writing with Symbols - it's old and they don't sell it anymore). I then go over this paper with my student before asking them to sign their name. I feel like this gives the student an opportunity to understand what is happening, instead of just writing his name on a paper because someone tells him to write it. Download this visual explanation here.
I also include this paper with the delegation of rights paperwork, in case it is ever questioned that the student understood what they were signing, at least this is proof that we tried.