Why are the Foreign Keys not showing on the ER diagram within my model?

The following would need to be performed to enable the Foreign Key within an ER Diagram:

1. Click on the Diagram menu and choose Diagrams to launch the Diagram Editor
2. Click on the Entity tab and check the following boxes: Display Logical Foreign Key (FK) Designator and Display Migrated Attributes 
3. Click on the Table tab for a physical model and check the following boxes: Display Physical Foreign Key (FK) Designator.  Also, if the FKs are not showing in physical side, then make sure that the Parent Table, Child Table and Relationship between them is not marked as 'Logical Only'.  Conversely, if they are not showing in the logical side, then make sure the same is not marked as 'Physical Only'.  
4. Finally right-click on the Entity/Table and select the Key Group Properties/Index Properties, in the  Key Group Editor/Index Editor check the box "Show FK Indexes" to show all ungenerated/generated Indexes regardless if the Relationship was not marked to generate.