It's the audio recording that matters. In Illinois, you can have cameras, no problem, but no audio UNLESS you post signage up about having audio video surveillance. This way even in public you're "notified" about audio being used.

In a sandwich shop, I might speak at a low enough volume a camera mic wouldn't pick me up. With no one around me to hear, the expectation is whomever I'm speaking to would be private, while in public, and they're not recording the convo either.