Creating a "NEW!" flag in Drupal 7 using entities and Display Suite

Have you ever wondered how to flag new content in Drupal? In a website I've worked on, I wanted to find a way to create a "NEW!" flag to flag new content. (Note: If you were only wanting to create a flag that says "NEW!" on the node page for the piece of content you can just use a view, but what if you wanted to have something that marks content as new in a list of node teasers?) Here's how I did it in Drupal 7 using a custom code field with Display Suite.

Problem: A flag or field was needed to display "NEW!" for new content.

Impact: Users won't be able to pinpoint at a glance the new content.