Add a reddit button to your posts.
reddit Button is a WordPress plugin that adds a reddit button to your posts.
The plugin lets you choose from all the reddit buttons and it is customizable as to where the button will show up in a post and on which posts it should be displayed. The plugin can also detect if a post is being referred to by reddit and have the button automagically show up on said post.
And, if for some reason you are not happy with the plugin's decision to show or hide the button for a particular post you can always specify where to show it.