Pins 
are 3D markup that you can use to indicate an area of your model that’s important to analyze. You can save pins to a snapshot and refer to them at any time.
Your pins are private in your model file, even if you share the model with others. However, you can easily share this information with others by adding the snapshot with your pin to a story. All collaborators with whom you share the story can see your pin and respond with comments.
For more information about stories, see Introduction to stories.