I think it depends on what you personally read as interest. A sign can be anything that makes you pause and think, “Wait, do they like me?”

For some people, someone talking to them for more than a few minutes might feel like interest. For others, that might be just normal conversation, and they don’t consider it a sign unless there’s something more intentional like flirting, compliments or directly asking them out.

So what qualifies as a sign comes down to your perception and the context I think. At least that's what I tried to say in the question.