Format Annotations and Labels (Formatting tags in Label Expressions)

Annotations and labels can also be formatted with VB script expressions.

Example: Parcel no. with numerator and denominator as two-line text

"<LIN leading='-1'><UND>" & [NUMERATOR]/1 & "</UND>" & vbcrlf & [DENOMINATOR]/1 & "</LIN>"

This kind of formatting can be taken much further.
The ArcGIS text formatting tags are used for this purpose.

For example, to explicitly set the font and height

"<FNT name='Arial' size='18'>" & [LABELFIELD] & "</FNT>"

or to set the text color:

"<CLR red='255' green='255' blue='255'>" & [LABELFIELD] & "</CLR>"

But be careful, because such text formatting tags always have the last word in formatting - no matter what is set in the annotation definition, the tags will override it!

An overview of the possibilities of label expressions and formatting tags
can be found in the ArcGIS Desktop Help.