My experience is that many straight men simply don't find men, ANY men, attractive and so applying that term to themselves just feels WEIRD. In fact, they may consider the male physique to be downright disgusting--hairy, lumpy, and just not any fun to look at. They understand that SOME men are CONSIDERED attractive by women, so they base their standards off those men and since they fall short, they assume they aren't attractive.
On behalf of straight women, allow me to set the record straight: do you shave? Brush your teeth? Bathe? Use deodorant? Wear semi-decent clothes? Have a job? Occasionally emit intelligent conversation? You do? You are f*cking adorable. SERIOUSLY. Stop comparing yourself to body builders and Brad Pitt. Most women think body builders are hideous (SERIOUSLY--they look like their immense muscles are about to burst through their skin and spray us with gore) and aren't interested in Brad Pitt because we know he'd never be interested in US in a million years. Talk about turn off.
And, no, we are not going to send you clear signals (or any signals at all) until we are pretty sure that you want us. We are trained from an early age Not To Hurt People's Feelings and to Be Polite and we know very well that there's nothing more emotionally stressful/disgusting then trying to shuck off a woman you don't want who is clearly interested in you. It is painfully embarrassing when guys do this to us so we try not to inflict it on anyone else. So if you are interested in a lady, you should start showing it right off the bat in a friendly manner that shows you are totally okay with being shot down since you are a Mature Adult and capable of Coping. Don't wait until you're f*cking desperate and have been f*cking yearning after your dream girl for 3 years--by that time the method you'll choose to express your feelings will be so fantastically outre and emotionally fraught that it will freak her out and end any possibility of there being a relationship. (Either that or a number of other equally bad things will happen depending on how you handle it--or she'll just turn out to be nuts.)
That, and NEVER EVER UNDER ANY CIRCUMSTANCES FORGET RULE #1, which is: ALL WOMEN ARE DIFFERENT. Everything I said above applies to me and possibly a fraction of the general female population, but THAT'S IT. (From what I can tell, I'm pretty vanilla sexually, but being vanilla does not mean that even a large fraction of the female population is like me, just that I'm approximately in the middle of the wide continuum that is female sexuality.) So if you're interested in a particular woman, don't start making plans or trying to fit her into some mental pigeonhole so you know what to do. Observe her, interact with her, see what she finds positive and negative and decide whether that's a good fit with the way you normally act. Women do actually forgive even major gaffes as long as you seem capable of recognizing that it WAS a gaffe.