If you see a random ad for a company on Google, click on it and then supply your email. Then they would know a lot more about than just your email. They would know every demographic filter they used to create that ad. That could be quite specific.
True, if the company only created one campaign and it was pretty specific, then yes, they could tie my signup to the campaign information. I'm not terribly concerned about this yet.
Let's say there's a SASS service you can tie into that has a massive database of browser fingerprint activity. Potentially you could get quite a significant amount of browsing history once enough websites are using the service. You can tie this to an email address etc. when a site requests a signup.
If you see a random ad for a company on Google, click on it and then supply your email. Then they would know a lot more about than just your email. They would know every demographic filter they used to create that ad. That could be quite specific.