Is this a sign she's interested or just niceness?

Lately, when I see this girl i like in the hallways she says hey or waves. This has been going on on a daily basis. I must emphasize that I am the one receiving the greetings not giving them and then forcing her to respond. Is she just being polite or is this a sign of interest? If shes interested, that's a great coincidence because i really like her. I don't want to come off as too presumptuous so your input is really helpful.