I think it’s unrealistic to expect that people not have an interest in someone unless they’ve met and gotten to know each other. People are attracted to each other physically, and that’s as good a jumping off point as any. It shows a certain lack of tact when people seem overly fixated on someone’s appearance, but that’s going to be how most people initially decide whether they’re interested. How we approach and present ourselves to each other is entirely a function of social norms, and I suspect a big part of the problem in Western society is that there has been a certain breakdown in those norms and what people consider to be acceptable behavior. I mean, with the note specifically: I am thinking specifically of one person I know who got a note from a stranger on the bus who would have followed up on it if she wasn’t attached.
With the exception of certain specific settings (e.g. certain bars, online dating, V-Day singles’ party) people don’t have a good handle one when, whether, and how propositioning members of the opposite sex is supposed to work. Hell, we haven’t even completely settled (as a society, not me personally) on whether it’s acceptable for women to hit on men. Class and race also enter into it, and more heavily than people are comfortable admitting. Propositioning someone outside of your social class can be an issue. All of this is to say, it’s complicated enough that people can be forgiven for awkwardness. I think that in general, people should behave in good faith, and with the ability to gracefully accept rejection. Beyond that, there really isn’t any way to define creepy.
“Creepy” as a concept is actually very interesting, since on the one hand, it defines a real sense of trepidation or caution in women that is a product of experiences with harassment. On the other it is an idea men use to articulate frustration with a lack of well-defined behaviors that allow them to be confident they haven’t transgressed this boundary, especially when the default interaction in our society places men in the role of initiator. It’s a real can of worms that makes me realize how glad I am to not be dating.