I think there's three main reasons for vague signals.
They legitimately don't know how they feel. Maybe they kind of like you but aren't sure. Recommended: do not pursue. Find someone who is enthusiastic about you. Do you really want to spend your time with someone who can't make decisions and doesn't know how they feel? It's exhausting.
They are afraid or uncomfortable, and are trying to avoid upsetting you. Like the comic. Enough men will do just that or worse if they get rejected that being polite can seem safer, even if it makes me man feel like he's getting mixed signals. You know you're not like that, but they don't. Recommended: same as above.
2b. You are talking to someone who can't leave like a retail worker. Stop bothering the person who can't tell you to fuck off.
They aren't thinking about you at all. Like one time they're happy to go bowling with you but the next time they blow you off on biking. What gives?? Mixed signals?? Nah dude she just likes bowling.