Shapes, Icons and Geometrical Constructs

Shapes.

Shapes are most often used as "dingbats" to emphasize pieces of text. But Mathematica CalcCenter treats them as letter-like forms, and also allows them to appear in the names of symbols.
In addition to shapes such as \[EmptySquare], there are characters such as \[Square] which are treated by Mathematica CalcCenter as operators rather than letter-like forms.

Icons.

Notation for geometrical constructs.

Since Mathematica CalcCenter treats characters like as letter-like forms, constructs like BC are treated in Mathematica CalcCenter as single symbols.