Currently SolidWorks does not have a native command to include subscripts and superscripts within notes. The workaround to this limitation is to use the Stack formatting tool when subscripts or superscripts are required.
When editing a note please locate the Stack command in the Formatting toolbar. Selecting this icon will open the Stack Note window.
From this window use the 'Lower' or 'Upper' text box to input the desired subscripts or superscripts (respectively), and select the second style option to remove the fractional line.