Let them know your intentions in a non degrading way and they will either accommodate that or they wont. Little effort and little wasted time.
This is really important, especially now a days. There is a careful line you can not cross otherwise you open yourself up to serious career consequences. You have to be good at reading female body language and facial expressions, not only to know when you are getting the green light and positive feedback, but also when you get a caution, or red light. You have to know how to pull back, being aggressive can be more damaging than helpful.
If you don't get a green light, there is NOTHING you can do to turn this around. The PUA pimps will tell you that it's possible to"game her" and "flip the set", which is complete BVLLSH!T. All you are going to do is waste your time, at best.... at worst be accused of sexual harassment. If you just met a chick you do not know who the fvck she is, you don't know who she works for, who her family is... nothing. There are three thing that can happen when a chick picks up on the vib that you want her:
1. Green light: She likes you and is interested. Get the number make a date.
2. Yellow Light: She likes the attention, but nothing is going to happen.. ask for the number, but don't be surprised if she flakes.
3. Red light: She does not like you and your approach is NOT welcome. Throw it into reverse and back the fvck out.
Rather than learning 'game' I would recommend to all men to learn body language. Knowing the difference between Red, Amber and Green is a lot more important than pretending to be confident.