You got to look at the whole content. Those smiles are just smiles, pictures frozen in time. And they are great, as long as they reflect your personality. On the other hand, you cannot be walking around with "sexy" or any other smiles all day long, that is just weird, unnatural.
[Added: By studying smiles (and body langugage) as Franco posted above, you can recognize different personalities. You can tell a lot about that particular person by just observing how he smiles, walks, talks, behaves,...]
When you look at the ocean, all you can see is waves. You can't really see below those waves, you can't see the depth and what is beneath. So those waves are like smiles, smiles are just surface of your personality. The depth of the ocean is your personality - what you feel, what you think, what are your beliefs, knowledge, experiences,...
You can fake lots of different smiles and perhaps fool many people. But girls in general have a good sense to see underneath those waves. They can discover the true personality very fast, some girls perhaps within minutes, if not seconds...
So you don't really want to fake those "sexy" or other smiles, that is just a surface. See, if you don't have sexy personality, sexy beliefs or sexy experiences, sexy smiles will not fix it. A girl will usually recognize in an instant sexy smiles and sexy body language - but the minute she talks to you she'll know right away you are not really that sexy, that you don't really have much experience...
Which is a problem, now she sees that you are faking something, and because she knows you are faking she may not trust you that much. She may be hesitant to go out with you, perhaps you might even come out as a weirdo...
Focus on the depth, focus on sexy beliefs, focus on determination to have sex, focus on playfulness, independence, leading, making choices, keeping the whole interaction light with no dramas... Focus on actions that lead to intimacy... All this will be reflected in your face and body language, your smiles will just be natural. She will look below the surface of your smiles, and she will see right away that you are sexy, that you are determined to have sex, that you are playful and interested, and that you can simply walk away if she is not trully interested...
Now she's got to think, now she's got to be more serious... She doesn't screw around with guys like that because she knows she could be dumped any day... She's got to make her choice quite fast - either have sex fast, or never see that guy again...
If you are a Nice Guy chances are that you are already smiling too much. You are too nice, too mellow, too compliant, and your smiles just reflect that you are a harmless. So you want to smile less, you want to feel more dominant, you want to make more decisions, you want to be more assertive and serious.
On the other hand, if you are a rebel, hard core bastard who doesn't care about anybody, or a guy who is too serious and stubborn, you kind of want to soften your personality. You want to learn to be more gentler and softer, more friendly, more smiling...
