Using the general ESRI Maplex Label Engine options to label compound polygons

Steps:

1. On the Labeling toolbar, click Labeling > Options.
2. Click the Maplex tab.
3. Check the Label only the largest polygon in a multi-part polygon feature check box.

If you want each part of a multipart polygon feature to have a copy of the feature's label, uncheck this check box.

4. Click OK.