She accumulating new clothes at higher rates than usual.

If your girl goes into makeover mode and tears through the mall like Sonic the Hedgehog on a mission, you should take notice. Most women have an affinity for retail, but if her shopping takes on a rabid focus seemingly out of nowhere, you should ask yourself why she has become invested in reinventing herself.

Again, it's about a departure from the norm. If your girl normally puts on a full face of make-up to run errands, don't think twice about her putting on mascara to go to the dry-cleaners. But if she's a sweats-and-Chapstick type of chick, and she suddenly starts taking an hour to get ready to go out (particularly, without you), you have a reason to worry.