You can use TeX formatting commands to include mathematical and other symbols and Greek letters in block diagram annotations. For example, the following model uses TeX commands in an annotation that describes the equation used for the model.
You cannot include TeX commands and rich text formatted text.
Double-click in the model where you want to add the annotation.
Enter or edit the text of the annotation, using TeX commands where needed to achieve the desired appearance.
Right-click the annotation border, and in the context menu, select Diagram > Format > Enable TeX Commands.
The text reflects the TeX formatting.