When you discover a new series and stay up for three days straight living off of poptarts and coke zeros just so that you don't have to waste time sleeping and you can catch up to the story. (I've only done this once... And I had a good reason! I'd just discovered that dub wasn't my only option and that you could find subs online. It was a three day weekend, so I had time to watch the whole series. XD. Then, after school for four days and falling asleep as soon as I finished homework I stayed up for two days to catch up to the fan translated manga!)
And when you get your family all hooked on the same ginourmous list of anime and manga you're hooked on.
Also when you start cosplaying at school, and lending out Akatsuki robes to your friends so that y'all can go as a group. (Me and my friends cosplay every Friday at our school! Although one of my friends wears an Akatsuki robe everyday that I got him for his B-Day...)
Best sign? When you get your prep of a cousin, who's friends all think that cartoons, especially anime and definetely shonen anime, is the definition of uncool, so hooked on Naruto that she becomes just as much as a rabid fangirl of Itachi and Gaara as you are. (it's REALLY freaky seeing a poster of Itachi next to whoever's the popular singer/ actor dude now...). And you get her listening to J-pop. :P
And you write fanfictions so often for your English assignments that your sensei now has a 50 word vocabulary of Naruto and Inuyasha and Death Note related terms.
ya... that's my personal accomplishments. Also posting a manga type drawing of yourself done by your artist of a friend for your Myspace and Facebook that your prep of a cousin insisted on you having.