It was User:pdf23ds. Here's the note. Excerpt:
I wish I could have been cryonically preserved. But suicides aren’t treated well enough for that. We get sectioned. I tried asking the cryonics places about options, but they wouldn’t talk to me. Fuck you, Alcor. Fuck you, CI. I might have lived except for you.
It means committed to a mental hospital. E.g. in Massachusetts the relevant law is in Section 12 of the chapter, so to "section 12" someone or just "section" them is to commit them to a hospital against their will.
Presumably he meant he can't go to a cryonics org or a regular hospital and just ask to be cryopreserved, because that would be suicidal, and voicing suicidalality would get him sectioned to a psych hospital.
Hmm. Good alternate explanation. Thanks.