As a Russian speaking person, I do not pay much attention on Bitcoin and bitcoin. Russian grammar does not have that kind of differences, and during English classes I dont remember that teacher put much attention on that kind of things (or same as you, "I have already forgotten about this").
When I write post, I try to concentrate more on tenses while doing Russian>English translation in my head.
After your topic, I think I would pay a bit more attention to Bitcoin/bitcoin, but frankly speaking, when I re-read my post, I wont click on edit button to correct this.
I don't know Russian but I think it is general rule for common noun and proper noun
Bitcoin: proper noun
bitcoin: common noun
BITCOIN: Capitalization of all characters (bad use)
BTC: can be accepted as acronym of Bitcoin (as proper noun)
btc: can be accepted as acronym of bitcoin (as common noun)