I don't know if sending messages via haircut is an efficient means of communication. Have you thought about sign language? Puppets? A pair of spoons and Morse code?
You should base growing your hair out, or cutting it, on how it makes you feel. Will long hair make you feel sexy? Feminine? Like a warrior elf princess? Then make it so.
I know that guys have preferences for hair. But they are just preferences. Any dude who would deem a hairstyle a dating "dealbreaker" is either a bitter, tyrant-like hairdresser, or serial killer who collects scalps.
As for what a hairstyle says about you... well, again, that would say more about the person interpreting your hair, than you. Is short hair slutty? Does long hair suggest Amish morals? Is it just hair?
Wear your hair in the way that makes you feel like a human firecracker.
For the record, I love both long hair and short hair, mermaids and pixies. I love long hair because of it's sensuality, and short hair because I am a pervert who finds long, milky necks sexy.
Hair length does send out a message, but more towards women than men. My friends and I have an irrational/rational dislike of girls with very short hair (excepting true pixies that would be overwhelmed by anything else), as they often exude a particular attitude.
We have all heard that men prefer women with longer hair. So women who choose to cut their hair very short are making a statement, that "they don't care what men think", etc. Also, for women under 30, it's generally not about ease, as they likely spend as much time taking care of shorter hair as they do longer. It is about a statement, about standing apart, being different, disregarding preferences, regardless of what looks best on them.
I don't think that there is much of a difference between mid and long length hair, except that long is more striking and a bit more elegant. Unless you're Audrey Tautou, Meg Ryan, or Halle Barry, short hair probably isn't for you. If you are very small, perhaps long hair would overwhelm you. Do what you want, but remember that girls will snap judge you long before a guy will.
Look, I have cut my hair short and grown it out so many times. I've had pixie cuts and bobs. I've shaved my head. I had a Mohawk. Twice. I tend to favor short hair and let me tell you, it has nothing to do with making a statement for me. I never feel sexier than I do with super short hair. With my neck and shoulders exposed, it is so cool and comfortable. When I have long hair I feel drab and frumpy and unoriginal. You say that is says I don't care what men think of me, but when I know I am being myself I can relax and be confident in my own beauty. What is sexier than that?
"We have all heard that men prefer women with longer hair." We may indeed have heard that, but is it the truth? I don't think so. There are plenty of men who like both short and long hair and given this, a woman who cuts her hair short doesn't necessarily to do it just to prove she doesn't care what men think. There are plenty of women with short hair who are just as sexy as women with long hair, and who feel sexier with short hair, as the other comment proves. And, let me point out that not all long hair is sexy. I've seen long hair with split ends, unbrushed, looking tacky...Sorry if I sound defensive but SUPERficial's comment strikes me as judgemental (not surprising given the admission to an "irrational" dislike of women with very short hair).
I've had a pixie cut, a shoulder length cut, and now my hair is long with soft curls. Personally, I feel sexiest when it's long; I can style it however I want, play with it when I'm bored, and flip it around when I'm talking to a guy. But every woman is different, I think it's more the confidence a woman exudes with whatever haircut she has that makes her sexy. Some women feel more confident with short hair, others with long hair.
Well, maybe I don't know a lot of porn stars, but if they're an indicator of anything (at least as far as fantasies go) most have long hair. I'm all for the "whatever you're comfortable with" hair, as long as it's not hair you don't bother cutting in 7+ years, because that just looks careless. Even dreadlocks need to be taken care of, otherwise they can become really disgusting really quick.
Though it's true not everyone can pull off short hair (I, for instance, have a weird nose that would stand out too much), if you can pull off short hair you could probably rock any look (take Natalie Portman in V for Vendetta or Domino) so in those cases it's really a matter of choice when it comes to what looks best on you. Regardless, you could feel more comfortable in hair that doesn't necessarily look best on you by society's standards and that's ok too, if you find someone with a taste similar to yours.
Where I live, if a girl has short hair, most people assume that she's a lesbian, whether or not it's true. Shoulder-length seems to be the happy medium--girly enough to appeal to the testosterone crowd, and short enough to not require much upkeep. One has more upkeep with short hair than with longer, surprisingly.
That said, wear your hair the way that makes you happy. Please yourself, not someone else. It's your hair.
Ok, I know I am late on this but I just had to mention.. your hairstyle DOES send out a message, but only in conjunction with your overall appearance and manner. If you are worried about guys getting a sort of message from your haircut, don't. Men can't understand what we are telling them even if we take the time to write it out in plain English for them; they just don't DO communication in any way shape or form. That said, some women will make judgements about your personality based on your hairstyle but what they think doesn't really matter anyway does it? The most important thing is that you pick a hairstyle that goes well with your face shape and makes you feel comfortable. The only exception to that rule is for certain types of jobs where having extremely long or very short hair could be viewed as unprofessional.