- In Europe a stop sign means that you have to wait until the way is clear. Of course, you normally don't have stops on more than two of the roads crossing. (Theoretically, you can wait forever at a stop, since people on the other roads won't stop and let you through)
- In North America (I've seen it in Canada), you have stop signs on all four roads crossing and you get through in a first in first out turn.
It seems to me that
- the US uses stop signs as a way to slow down the traffic (so, no real meaning), but
- in Europe it does have a clear meaning: "it's dangerous to drive over a crossing without halting". Not only you have to be careful because you have no right of way (the "give way" sign) but you really have to stop and look at the traffic, mostly due to poor visibility (or high difference in speed).