Guys don't start thinking I'm gay for noticing this lately, but I am 4 for 4 on guessing that a girl has gotten a new haircut...
2 Of these were friends of mine and their hair was noticeably shorter so no big deal...but there have been 2 other girls that literally when I first met them I asked "Have you gotten a haircut in the past 2 weeks?" And sure fuckin' enough, they had!
HB's: "How did you know that?!?" Immediate IOI's!
Shreder: "You just have that new haircut vibe about you!"
If you just take some time to notice things you can really add some cold reading (or hair reading in this case

) techniques!
Some things to look for if you want to try and use this: If it is noticeably "brushy" around the bottom (like the end of a wider-style paintbrush) especially if she has shorter hair. She has no split ends: trust me this is fairly easy to see from conversational distance. If her hair is noticeably "pronounced": like if her bangs are really in place.
Also, more often than not you can kind of just tell because she just has a really clean/fresh looking haircut, and if you know anything about women, they will just eat this up! Doggy Dinner Bowl Look for sure!!!