Unless, of course, its 18 inches long and prehensile…
Advice here from another veteran of your situation …
Better make some decision soon, y’know? Remember, she’s calling you! Jeez, most guys would kill for that! Does she introduce you to her friends/family/coworkers as ‘my friend, morkfromork’ or simply as ‘morkfromork’? Does she compliment you a lot? Does she laugh at all your jokes? Even your stupid ones? Does she casually touch you often? This isn’t to say that every girl who touches a guy is interested, but to most, touching is an invasion of personal space, and she won’t do it unless she’s really comfortable around you.
Calls, touches, compliments, fun … I think I’d take another look around for that BRIGHT NEON SIGN I hear buzzing! 
Think about this: if she IS interested, and you’re second-guessing her ‘signals’ because they’re not as obvious as you’d like, then chances are that if you don’t make a move of some sort soon, she’s gonna lose interest fast because she’ll get the impression you’re not interested. Welcome to Friend City … you’ll get to hear all about the gory details of the next guys who did make a move. Since you’ve been seeing each other pretty consistently thus far, I’d have to say three weeks is probably on the dangerous edge here.
All the advice so far seems dead-on what I’ve found. You’re gonna have to ask her out for a real date. Then, at the end, go for the kiss, planted right on the mouth. It will be intimidating, but whatever you do, don’t hesitate and don’t wimp out. I wimped out at the perfect opportunity once, and found out, after the fact, that was her deciding point … I was to be just a friend. :smack: Let this happen to you just once, and I promise you’ll definitely learn that is one too many times. So, just move for that kiss on the lips. Her next move will tell all. If she turns away, you’ll know precisely where you stand. If she’s interested, she’ll reciprocate with receptive action, and your (apparent) confidence will really, really turn her on. I know it’s cliched, but the biggest risk is not taking one.
I really can’t elaborate any further on what Giraffe and micahjn have said. They’ve hit the target.