On WordPress.com you have the option of creating a Follow button, very similar to Twitter or other social networks. This button will allow people who click on it to receive e-mail notifications whenever you publish a new post.
If you’d like to add it to your WordPress.com site, it’s available as a widget that you can simple drag into your sidebar.
At the Generator you’ll see that you need to enter the URL of the blog you’d like to create the button for, which in most cases will be the URL to your WordPress.com blog. Next, there are a couple of options to choose from. Choose whether you’d like to show your current follower count next to the button, and whether you’d like to show your blog’s name in the button text. Also, choose the default language you prefer for the button.
This is how the button looks, with and without your follower count:
Embed a Follow Button for Your Blog (Hot Off the Press, Oct 30, 2013)