The yellow bar at the bottom of a query indicates the presence of a query comment. Query comments can be edited from the query design screen by clicking on the Query tab near the top of the included fields section of the screen. After you've added a query comment, be sure to save the query to a workspace by clicking the "+" Organize button in the upper right corner of the screen.
Query Comments are a great way to preserve instructions for queries that are not looked at frequently. All users with access to queries have the ability to add query comments.