In this picture the symbols IIIUVIUV is written on the side of the boat. http://img345.imageshack.us/img345/2047/blueboat0vi.jpg
What does it mean? (people with boats I'm looking in your direction)
Is it further proof that the Losties come from a place other than the real world and that the Island they are now on is the real world?
I have no clue about the boat. However many cities create their own signs.. There are a lot of cities where there are signs asking you not to blow your horn. They are usually in neighborhoods or hospital zones.
In fact you can get a ticket in Moscow for using your horn in a non-emergency.
Ok re the "no horns" sign. I know that since Sun is walking her dog the scene was supposed to be in Korea, however I assume it was filmed in the Hawaii. It makes sense to have a no horns regulation next to a park or hospital. In any case We are getting too specific by looking for the entire sign. The standardized parts of the sign are the red circle with a slash indicating a prohibition of some sort. The emblems within the slashed circle vary from location to location. I have seen “P” for parking, a picture of a cell phone (next to a hospital), a dog silhouette and various other prohibited items. The horn picture is not a standardized part of the sign and will probably not show up in any DMV manuals..