[invalidusernam3]

That's not really a use case for [sic]. As per wikipedia: erroneous or archaic spelling, surprising assertion, faulty reasoning, or other matter that might otherwise be taken as an error of transcription.

[Hoasi]

One or both of these use

> archaic spelling

> other matter that might otherwise be taken as an error of transcription

fit the description though the case for archaic spelling is arguable.

[invalidusernam3]

Both the US English and British English spellings are used extensively, nobody would think it's a spelling mistake. And calling British English archaic is quite insulting, it would be like calling US English "dumbed down".

[jimmaswell]

AmE and BrE are both used simultaneously in online spaces. Neither needs to be corrected or (sic)'d to the other.