For vertical text, there's no simple setting. You can make the string indicator only as wide as a single character but you have to be careful about different fonts. Captions for controls and indicators can be stacked vertically - just show caption and then right click on the caption itself to select Vertical Arrangement. You could choose to hide the indicator itself and write your string values to the control's caption using a property node.
If it does not have to be a string indicator, you can easily center the text either horizontally and/or vertically with a picture control. I have attached an example.
