Here's a clue...Attorneys are a little local clique. Same place, same group day after day.
My guess is that there was some kind of Christmas party and that's where he signed the book...(if he did in fact). Look in the book for other non-student signatures.
Why did it say "Christmas 1977". It was a 1977 yearbook. Did she add that, too?
Notice he didn't address her by name...Just to...cuz he didn't know who the hell she was.
Since it signed with same suffix (D.A.)
I bet he never signed it at all and that the signature is total forgery. Copied off her Divorce/custody decree.
He never signed anything with D.A. suffix, only done by his secretary.
She may find herself in a heap of trouble over this eventually.