FYI: For your information
So, if you regularly read my posts (God knows if anyone does), you have noticed that I have not been as on-the-ball recently. That's because I have an almost-6-month-old. He's a handful. Anyway, just wanted to let you all know (all two of you? maybe just my dad) that I'm still trying to plug away, but I have abandoned the idea of posting daily. To be honest, I haven't been doing that in quite some time, so the real news is that I am abandoning my practice of going back and populating past days with posts so it looks like I write daily.
FYI is first attested in 1941 in the Washington Post, though they were just explaining the title of some program called, well, FYI. Since it was already the title of something before it ran in a newspaper, I would guess that the initialism was around for a little while beforehand.