I haven't done it myself but found out how to do it in 30 seconds, its all detailed in the help file, go to:
Using CitectSCADA > Graphics Pages > Configure Graphics Pages > Menu Configuration Dialog Properties
And
Using CitectSCADA > CitectSCADA Projects > System Projects Reference > Defining page menus
In there:
Symbol
The symbol to associate with the menu entry in the format of <library name>.<symbol name>. The template expects the symbol to be a certain size when it is configured against different menu types: For tabs, symbols are 16 x 16 pixels. For buttons, symbols are 32 x 32 pixels. Some common symbols can be found in the symbol libraries of icons_16x16 and icons_32x32. The field is not applicable for menu and sub-menu items.