Heck, I've been mistaken for a girl too usually because of the AwwLilMaggie name I had. But I then have to post my real name to correct them.

I've since changed my name which eliminates that problem.

Hm... It's interesting topic. What about me, the most popular nickname which I use is user... or guest.  I think, that people don't like such nicks: they are not friendly or nice or,  maybe, names at all. But I've never try to think about other ways to introduce myself. (Login for LTS was only a good email address, which people, who know me, don't forget.) So, nickname for me isn't important. - it's like an id.  But I have met with people, who like, when  they called by nicks... someone didn't tell me his real name.

And I don't use avatars.  In my opinion, pictures, which you find in internet aren't original and can't say anything. (So, make it yourself =) .) But they can give pleasure to you and another. (For me, I can't find any pictures, what I want to use as avatar). But if avatar can be only nice picture for owner, can we take it seriously? - We can judge tastes of the person only. So, avatar isn't important too.  Such opinion about subscriptions. 

You are right, when you estimate the person under his messages. But the first of them very often aren't as good, as they can be. In the first time people should get used to conditions. So, true opinion  about the person, can be found only some time later, after you can speak with him.... and in real life, when nickname and avatar are not so important...

I find the avartor and signature practical.

1. I wasn’t able to use exactly the same name on Deviant Art. So I hope people recognize me by the avartor.
2. On some forums I am sort of like a ghost, only posting occasionally.

Sometimes people put something in there signature that tells something about them, but in most cases I don’t think you can learn that much about a person by there signature.