By using an Annotation, you can display the weight of your assembly (or part) in the graphics window, which is awesome for when you are making design changes or optimizing it for weight. Here is the procedure:
1. Insert > Annotations > Note
2. Drop the annotation on the screen where you want, and then over in the property manager, select the Link to property button.
3. Choose the File properties button.
4. "Weight" under Property Name, and "Mass" under Value / Text Expression, and then OK.
5. Back to the "Link to Property" dialog, use the pull down to select "Weight."
6. Here is an example of the result (the 164.11). You can add text around it and change the Font format as well.