As lots of people have pointed out, it could be due to the avatar. Not just for having a girl in your avatar/sig .., I think it's more the fact that your avatars/sigs (Organic Beauty Sig as an example), are pink and soft.

And your name involves "Sakura", which is a girl's name in Japanese.

...

It'll be a combination of lost of things.

As with sparker, I think, one big factor is posting/having a lot of stuff which could be classified by some people as "cute". In Western society, cute seems to get linked up with girls a lot.

Like this kind of stuff in posts -» =♥_♥= nyuu!!! =♥♥♥_♥♥♥=
Like this kind of stuff following posts -» :3  ^__^  Kawaii~  uñyaa~
And this kind of pictures-»