On the general map, showing the 1000 bigs, there are 60 different icons with an " ! " in the middle of the icon, meaning that those bigs are in zone +. That means that these climbs can be claimed but lead to the eurobig (all the 1000 in Europe) and not to the superbig (940 in Europe and 60 out of Europe). Be careful by choosing to climb those bigs.
For all better explanations, look at the page zone + .