1) You know you're a writer when the voices in your head are seeming more and more real as you continously scribble down what they are saying, until you are almost certain that there is some entity dwelling inside your head, a parasite giving the host inner guidence to follow in exchange for a little food and comfort.
2) You know you're a writer when you use weird random metaphors that may or may not make sense to describe how you're feeling at one particular moment.
3) You know you're a writer when there are marble-sized callouses on the sides of your fingers. (that is, if you don't use a keyboard to write, lol, but don't forget carpel tunnel!)
4) You know you're a writer when you stay up in the wee hours of the morning, describing the strange and frightening creatures that probably are lurking in the basement, and explaining what their favorite hobbies are.
5) You know you're a writer when the most mundane things imaginable are instantly turned into poetic, bizarre, or even disturbing things the moment you think about them.
6) You know you're a writer when you consider Writer's block as a real medical ailment.
7) You know you're a writer when you try to address people in a narrative tone, just to be funny or to amuse yourself. "And as I opened the door, there stood William. His crisp green sweater vest seemed like a living thing constricting upon his chest, and the grotestque zit on his face oozed something repugnant and vile. (Okay, I admit it. I've never done this, but, come on! Our thoughts are sure babbling in such a way)
8) You know you're a writer when the characters in your stories begin to appear right in front of you. Unless you're tripping out on some kind of drug and hallucinating, and in that case this may not apply.
9) You know you're a writer when you save your essay/assignment for the last minute because you wanted to finish explaining just why Joe got murdered by the demented psycho with the stapler in the treehouse, or whatever the heck happened....
10) You know you're a writer when words are your solace, your refuge, and even if others think you are weird and somehow not quite right, you wouldn't have it any other way!