What does it mean when a Girl holds the door for you?

We've been seeing each other in the gym for months here and their.We came at the same time and I was 9 feet away from her.She opened the door and let me go in first.I said"thanks!"and she looked for just a quick second in my eyes and then my chest cause my nickles was out and said"uh hu"without smiling.I remember I holding the door for her a month ago and she said"Oh Thanks!"and smiling.I do like her a lot and idk if this was a sign if she's interested in me..help!