Using the Watermark property you can provide contextual clues of what value users should enter in a C1MaskedTextBox control. The watermark is displayed in the control while not text has been entered. To add a watermark, add the text Watermark="Watermark Text" to the <c1:C1MaskedTextBox> tag in the XAML markup for any C1MaskedTextBox control.
So, for example, enter Watermark="Enter Text" to the <c1:C1MaskedTextBox> tag so that appears similar to the following:
<c1:C1MaskedTextBox Height="23" Width="120" Name="C1MaskedTextBox1" Watermark="Enter Text" />
If you click within the control and enter text, you will notice that the watermark disappears.