For example, if after some conversation she's standing beside you and returns a smile, you might offer her a light hug around the waist or run a hand lightly down her upper back. How she responds will tell you a lot. This doesn't mean that she jumps you in the middle of the cubicle farm. If she doesn't react at all, proceed but with caution. And part is, on some level, a desire for plausible deniability in case the guy doesn't respond.
Women have egos, too.
Once you've reached the point where you're both comfortable touching each other in a semi-sexual way, we're out of the pickup script and into the mating dance proper.