property FormatConditionalAppearance.Underline as Boolean
Underlines the text.

TypeDescription
Boolean A Boolean expression that specifies whether the text is underlined.
By default, the Underline property is False. Use the Underline property on True, to show the objects underlined. The Expression property defines the conditional expression that determines whether the current format is applied on the pivot's cell based on the cell's value.

The following properties can be applied on objects:

Also, the decorative text is allowed as following: