It's S.B.T.C. (Shall Be The Conqueror), not SCTC.
It is meaningful to look at as a factor, since he made such a point of words with those beginning letters when he signed the yearbook, and a long time later he confesses to a murder in which a "ransom note" is signed at the end with the deliberate letters, S.B.T.C.
If investigators did not consider that meaningful enough to take a look at its possible connection or significance, they wouldn't be doing a thorough job.
He's still writing to Tara but this is written AFTER he has signed his name and he has totally changed the subject: "Sometimes, so blurred by my own eyes, I've seen the best things come and go simultaneously";
During one of his interviews overseas they quote him as describing the encounter as a "blur".
We have blurry vision here on FR sometimes....It's when we're crying.
So, the guy has his own language......like most of us do.
That yearbook seems really, really important as to as "how he thinks", "How he writes". He may have even kept his.