If the universe is finite shouldn't there be warning signs for spaceships when they are nearing the end?

Indeed, the universe is finite, but it is constantly expanding. However, theoretical physicists--people who study abstract applications of physics such as black holes and the like--have figured that if a spaceship were to start from Earth and travel in a straight line forward through the universe, there would be a point when it would come to its starting point. Therefore, the universe is a "hypersphere", a 4-dimensional sphere (the dimensions being height, width, length, and time). It is possible, therefore, we will view the Voyager and Pioneer spacecraft sometime in the near future! (But since the universe is expanding, there is a possibility that we won't see them ever.)