Need help creating a plugin to add an icon to each post title

I would like to create a plugin that would add a very simple icon – a small green, or red circle, to the title of each post.

More specifically, this icon represents the content of the post. For example, if the plugin finds a keyword “foo”, then the icon color in the title becomes green. If there is no match for the keyword, then the icon remains red. Is there a way to implement this? In addition, each post already has a category icon, so this is not what I’m looking for.

This picture shows what I want to achieve with this plugin:
Picture

I realize this probably will need more clarification, but that is the basis of what I want to do.