Should you hug a girl you know whenever you see her?

Realistically speaking I'd say No. Just because a girl hugs you every time they see you doesn't directly mean that they like you. In Europe for example many countries' custom for greeting a friend is to hug them!

It depends on the type of hug though too, if it's a tight hug that seems to linger longer than usual then it would likely mean something...

The good news however is that it does mean that they are comfortable with you, so while it doesn't mean that they like you it probably means that they are more fond of you than a normal acquaintance.