To be honest, and I am going through a situation of liking a girl (thread about girl losing interest), guys are rubbish are probably rubbish at giving signs in their 1st experience of liking a girl. First time I have really liked a girl and I am not good at giving signs.
The problem is, asking her out with my mates, asking her about herself/her family, maintaining eye contact, mimicking her behaviour, etc (all this and more we do to each other in my situation with a girl) is all good but you run out of ideas. The only ideas left are too say compliments (also done between us and I made it obvious). If the boy doesn't react badly at all then you know he's comfortable with it. Or you can make physical contact, but you need to know you are allowed to. The other person has to tell you it's ok.
Put it this way, both people have to be confident and up front and let each other know it's ok if you're going to get physical otherwise you run out of ideas to give signs - everything else gets repetitive. Also, it puts a person off asking the other out if the other gives no signs. Where is the encouragement for the person (usually a boy) doing the asking? At least with some solid signs the person will know there could be a chance here for something happen.
So signs matter. But what also matters is if there is a vibe. Step back and think about body language, how the other person acts. For example, the girl in my situation is "inviting" by showing me a photo of her as a toddler on her purse, asked questions about my likes/dislikes, even shocked I was a month and a bit younger then her. It is obvious from how enthusiastic and vibrant she was that she likes me. When you get setup or are close mates to someone, there is none of this, just the odd "sign" meant as friendship - like physical contact but no special "atmosphere" or bond can be felt. This is the problem with signs, a lot of them are what mates do with each other. Unless, of course, like me, you get a whole package of them.
And I don't agree that if a guy leaves asking out a girl for a while, that is because they are incapable. There's hundred and one reasons to take time - not even anything to do with the boy or the girl in a given situation. It's not as simple to just go up to a girl and tell all. It does take some balls.
So unless the boy gives more then just one odd sign, even seems worried, trying to break the physical barrier, then you know he likes you otherwise it's hard to know (signs being like what mates do). Otherwise, it's hard to know. This is some of how I act when I like a girl.