A friend of mine used to be an office manager, and was sometimes the last person out of the building at night. There was a bit of a walk from the exit door to the parking area.

She would look around before/while leaving the building. If she saw any guys hanging around, she walked like she was angry, cussing softly to herself.

It always seemed to work (she's retired now). Even when the guys passed close to her, they didn't seem to want to take on a woman that was PO'd to start!