External Follow Button
While there are several ways visitors to your site can follow your WordPress.com blog, you also have the ability to create a Follow Blog button that can be added to external websites. This button will allow people who click on it to receive e-mail notifications whenever you publish a new post on your WordPress.com site.
In the Generator, you will need to enter the URL of the WordPress blog for which you’d like to create the button. Next, 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 for the button.
This is how the button looks, with and without your follower count:
Embed a Follow Button for Your Blog (The WordPress.com Blog, Oct 30, 2013)