I've looked in the User CP before, yet even when I search via CTRL+F I can't find it.
Perhaps CAG Newbies don't gain this function until the first 30 days are up? That is the only thought I can think of about it.
Edit: I just checked the FAQ and it is almost as I thought. I can create a signature, but only of a single line of text for my first thirty days here on CAG. Does anyone remember how to create this proto-signature?