Good question, but I don't think that's a feature here. if so, that's news to me!
The only thing I can think of is perhaps to build your own mailing list or something. I'm doing this on my paid focus group hub, but I don't know if this is what you want to do.
Also if your visitors subscribes to your RSS feed, then they will see when you have new content published. (Your RSS link can be found in your profile). You can tell visitors to go there and subscribe to your feed - or you can take your RSS link and add it to your hub and tell them to subscribe from there. Hope this helps!