If Karr had actually used "SBTC" in the yearbook, it might be significant. However, he actually wrote, "Though, deep in the future, maybe I shall be the conqueror and live in multiple peace..." All this really proves is that Karr once wrote a sentence in which four consecutive words happened to begin with "s," "b," "t" and "c." Big deal. I'll bet that there are thousands of posts on this site in which users have written four consecutive words that happened to begin with "s," "b," "t" and "c." I strongly believe that Clinton lies, for example.
All this really proves is that Karr once wrote a sentence in which four consecutive words happened to begin with "s," "b," "t" and "c."
The word "peace" was actually below the word "multiple", which suggests to me that it was a valediction (i.e. conclusion to the note). By saying that he "shall be the conqueror and live in multiple", he seems to have been hinting at his intent to live secret lives characterized by grandiously perverse behavior.
The people who assume that Patsy Ramsey killed her daughter based on the ransome note seem to making the mistake of assuming that the murderer didn't want to be caught. Assuming he did it, Carr seems to have wanted to have been tracked down and caught from the beginning and thus the obviously phony ransome note with hints of his identity, his correspondence with strangers regarding the crime, and his high visibility as a grade school teacher.
In any event, the DNA evidence should either convict him or rule him out if it's been well preserved.