I was talking about myself... if I'm joking (or it's a joke in itself), I use parentheses and smileys, but if it's a normal post, I don't use anything.
although there are exceptions, and I sometimes use parentheses in normal posts (for example, like today about movies)
P.S. as for others, I don't know how they do it... I've seen posts with a lot of parentheses, but they're not funny at all.