We have already seen how to have icons for the toolbox items. However, unfortunately, it is not the same way for the icons on the designer surface.
Good news though, it is not that difficult. As we create our ActivityDesigner, we essentially need to add the following property:
<Rect Location="0,0" Size="25,25" ></Rect>
<BitmapImage UriSource="Activity-Monitor-icon.png" ></BitmapImage>
Hope this helps!