An emoticon used to express slyness or sarcasm, showing a pretty serious face.
This emoticon is mostly used by Latin American Internet users, since the ¬ symbol is easily typed by pressing right alt (in the Spanish keyboard Alt Gr, which is like pressing Alt+Ctrl at the same time) and 6 in the Spanish keyboard.
The alt code for ¬ is Alt+170.
me: I'm bored. Wanna rent a movie?
gf: Yeah, that'd be nice.
me: What do you wanna watch?
gf: I heard Eclipse is out on DVD today.