Time: 11pm approx.
Location: Bar.
Description: Place is almost empty except for a few people. At the bar
is a good looking blonde. She has her mobile and keys on the bar and
is talking to one of the staff. She looks like she could be calling
somebody.
Immediate thoughts: She's been waiting for someone and they haven't
turned up so she's pretty annoyed. She has her mobile phone because
she's trying to call someone to drive her home (all this entered my head within 3 seconds)
My reaction: Didn't approach as I thought she was annoyed. Also her
talking to the bar staff put me off as I didn't want to approach with
the bar staff watching.
Possible approach: Walk up and say "Did you get stood up too?"

As a side note I posted this else where and one of the answers I got was that women go to bars to relax not to be picked up. True or false?

Women can go to bar to relax or be picked up, you will never know unless you approach her. Not all women are the same. Start approaching so you can get over your fear of rejection!

Girls out alone are really rare, but is also the easiest pull your gonna get. When you approach girls that are alone, never insult her about it. In fact, you should compliment on her about it. They are already feeling awkward about being out alone. Don't even bring up the fact she is alone until you build little bit of comfort with her.

Thinking about it I was probably just making excuses in my head. The universal "Hi" would have been good. Hell, she might have even enjoyed having someone to talk to.