Tactile Icon - Cup/Beverage
The shape is like a tea cup, wider at the top with an indent in the top middle, narrower at the bottom, and a little bump on the right side representing the handle.
This icon was created for the beverage feature on many North American microwaves. It started as a mug - a tall rectangular shape with a bump on the right side. That was too generic and square. Then the base was narrowed and a little dip was added to the top. The next iteration is what is displayed, a shorter shape, a more prominent dip in the top, and the nub on the right.
Once people are accustom to the location and shape, they don't explore the entire shape. A notable edge is all that is needed to identify the tactile icon. In this case the notable edge is the top dip. It is smooth and fits a finger well.
This design is obviously directed towards coffee and tea beverages. At some point icons may be needed for other beverages such as beer and wine.