Adding Control Decorations - UDIG Developer Guide - User-friendly Desktop Internet GIS

To add a decorator to a label (the 'x' and '!' that appear with warning and labels) you can use the ControlDecoration as shown here:

final Image fieldDecorationWarningImage;
fieldDecorationWarningImage = FieldDecorationRegistry.getDefault().getFieldDecoration(FieldDecorationRegistry.DEC_WARNING).getImage();       
warningDecorator = new ControlDecoration(label, SWT.LEFT | SWT.CENTER);
warningDecorator.setMarginWidth(4);
warningDecorator.setImage(fieldDecorationWarningImage);
warningDecorator.setDescriptionText("Warning!");

To show the label decoration:

 warningDecorator.show();

To hide the label decoration

 warningDecorator.hide();