Its the writer demonstrating that he/she is repeating the words of the initial writer (or speaker) exactly as they appeared (even though the spelling, grammar or fact may be incorrect).
Not sure I've explained that correctly but hope it helps. I also wish I was funny enough to write a witty response using the (sic) reference but I'm tired and need to go to bed.
Now, anyone copying what I've just written would write 'FredPuli wrote "That's correkt! 'and then put (sic) after it to show they are copying exactly what I wrote, there's no printing error and nor are they themselves mistakenly spelling 'correct' as 'correkt' :
FredPuli wrote "That's correkt" ' (sic)
Sic, here, is Latin for 'in that way' so the copier is writing 'wrote "That's correkt "(in that way)