code: public ESigItem add(ESigItem item) {
          if (!items.contains(item)) {
              items.add(item);
              fireEvent("ADD", item);
          }
          
          return item;
      }
docs: Adds a sig item to the list. Requests to add items already in the list are ignored. If an
  item is successfully added, an ESIG.ADD event is fired.
  
  @param item A sig item.
  @return The item that was added.