Menu: View→Object Properties→Text→Font style
If the currently selected object is a variable, this is the font style used for its name.
(See To change the font for a variable name.)
If the currently selected object is a figure caption, this is its font style.
(See To change the font for a figure caption.)
Programming
In Amos Graphics programs, you can select the first item in this ComboBox as follows (Visual Basic):
Dim aComboBox As Windows.Forms.ComboBox = pd.GetComboBox("", "VariableStyleCombo")
aComboBox.SelectedIndex = 0