'Sic' actually means 'literally' or 'as it was written', from the latin 'sic erat scriptum' - 'thus was it written'.
It allows you to quote something with an error or quirk, and to denote that you're quoting the error or quirk verbatim - showing that the error is not yours.
Sic is also used derisively to denote errors in others.
https://en.m.wikipedia.org/wiki/Sic
I think that option 3. above is the most elegant - clear without getting too 'up itself' It also follows how you would phrase this in computer logic, rather well, yet is simple:
"...suppose I write a letter from me [sic] to you." [sic]
Hope that helps,
😊