You know you're a writer when you can identify with all of the points made above.
You know you're a writer when you spend your time reading said points and going :O That's Me!!! rather than studying for the two-and-a-half hour Statistics exam you have tomorrow and will fail if you don't prepare. *Guilty*
You know you're a writer when you punch a hole in a mirror and your dad says "Writer's block?" without even looking up from the TV.
You know you're a writer when you look at someone on the bus and think, "Now, how can I change that person's life into a novel?"
You know you're a writer when you go over your older babies(stories) and suddenly panic, take out a red pen, and scrawl all over it, correcting grammar and spelling, and develop the wording because your style four or five years ago truly sucked.
