It is a hardiness zone map for plants. Canada has one too that is similar to the USDA zoning map. The higher the number, the warmer the climate is. Here is a link to see all the zones for the U.S.
I see...mine can be in various zones...wiki says its 10a while some portuguese sites says 9, without any letters. But looking at the temps scale I think 10a is accurate.
Zone maps do vary. If you want to show one just pick something you think is close. It does at least gives members an idea what your conditions are like when they are giving your advice.
I'll also add that unless you are in a more tropical area, the zone is more-or-less meaningless to orchid growing, as we tend not to grow them outdoors.