I think many women have trouble sending signals of interest. It could be for a variety of factors. Many attractive women just come to expect men to express their interest. Sure, they shoot down a ton of men in their prime. Grow a pair. Get over it.
If you meet a women who is confident, outgoing and assertive in that specific environment, yeah she might send a signal. Is it assured she will signal if she is interested? Absolutely not. There's a guy around the next corner who will make a move and another after that.
My experience is that no matter how many times we are told it's different now, men are expected to take the lead. When I'm clear of thought, I always tell myself that. It works. By virtue of this, I've met some attractive and interesting women in unexpected places. Places where the women I met were not at all expecting to meet someone and had no idea until I initiated contact and assertively pursued.
Now of course that makes it sounds simple. It takes communication skills, resiliency and working toward your strengths.
On the flip side of this, when a man makes a move a women will clearly send a signal back.
1) Alright, I'm interested. Let's see where this goes.
2) Okay, I'm not sure. I'm intrigued a bit. Maybe there's something here.
3) I'm not interested.
The results of 1 and 3 are obvious. No. 2 is very dicey in the sex and romance department. It's not necessarily a total time waster. I've had fun with some of these women. Some became friends and I have dated their friends. Expanding your acquaintances and social circle is never a waste of time.
Note: No. 2 could also have a subset 2b. Okay, I'm not sure. I just broke up with my boyfriend. We still hook up once in awhile, but I really need to get out there. These relationships can be fruitless especially if the woman continues to send mixed signals. If the woman uses you for rebound sex or simply an experience and heads back to her BF, take what she has generously given you even if it's not her heart.