I have recently put a Subscribe to feed banner under the posts which encourages the user to Subscribe by feed or email in a very sleek way. You can also put a banner like that very easily.

Here are the steps:
- Open Single.php
- Find the content call function
the_content - Put this code under it:
<div style="padding:5px; border:1px solid #999999; margin-top:10px; background-color:#FFF8AF;">
If you enjoyed this post, make sure you subscribe to my <a href="RSS LINK HERE">RSS Feed</a>
</div>
You can customize its appearance as you wish. You can set the border, the background color or you can simply add email subscription link too.
These kind of banners provide a simple push to the visitor to subscribe to the site and thus are quite useful.
Thanks to Jai
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