I found this a somewhat interesting read – over five hundred individuals in Japan were polled by the Mobile Marketing Data Labo, providing these insights into how folks can spot otaku.

They are using otaku slang, net jargon or 2ch cant

They just happen to have anime/manga/game goods about them

They respond to otaku type keywords and issues

They become very intense when the conversation turns to anime/manga/games, and only then

The tunes they hum are all anime related

They know excessive amounts about a given anime/manga/game

You can somehow just tell intuitively that they are an otaku

They talk unconcernedly about anime, manga and games all the time as if it were normal

They start talking about a seiyuu

They are carrying a bag from an otaku shop like Animate or Tora no Ana

Out of the 10 points above, do you commit any of them?

It’s somewhat interesting that these are the ways that you spot an otaku. To me indulging in the anime world is like a hobby for me, something I enjoy. Just like how a normal guy would enjoy watching soccer, we call them a soccer freak. But for people like us who enjoy watching anime, we’re called an otaku the moment they hear the word “anime”. I don’t see how talking about a seiyuu makes me an otaku, it simply means that I love the VA a lot to want to talk about her :D.

Well looking at the 10 points above, I only remember doing #2, #5(sometimes), #6, #8, #9

#8 is a little exaggerated though.

Source: MMD研究所 via Sankaku Complex NSFW via Kotaku