Edit:
As pointed out by @NicolasMiari in the comments:
This no longer works after iOS 7, as the bookmark button appears inside the line text box.
. ( ), " " ". :
[_searchBar setImage:[UIImage imageNamed:@"My-Custom-Image"] forSearchBarIcon:UISearchBarIconBookmark state:UIControlStateNormal];
:
- (void)searchBarBookmarkButtonClicked:(UISearchBar *)searchBar {
NSLog(@"click");
}