Most Helpful Girl
Here's THAT list! :P
She finds reasons to initiate conversations with you, especially about non-weighty topics, when you have not addressed or talked to her first. This is a false positive if she initiates conversation about a specific work topic (if you are co-workers) or if she is talking to you in her job as service personnel (e. g. checkout line or waitress).
She invites you to things, like little meal outings to get food or meaningless little trips (e. g. pick up something at a convenience store). This is a false positive if she is a habitual social-engineering type that tries to make everyone feel included, but this "type" of person can usually be easily identified in a group.
She touches you. Unless she is the type who touches everyone (easily observable), then if she is, in addition to making lively and vivacious conversation, touching you, this is a positive sign.
If you ask her to join you in doing something (e. g. casual lunch, coffee run) and she is unable to make it, she suggests another specific time/place. This means that she likely had a real conflict but does not want to let the opportunity to interact with you slip away. If she is not interested, she'll just say she's busy or at most say "another time" unspecifically.