Answer: ship contrails.
Yes, ships will leave contrails as they sail along just like a plane will do when it flies through the sky high enough for the water vapor from the engine exhaust leaving the nice white trail. The image on the right was taken yesterday (March 5) from the new NOAA-19 satellite that was recently launched. (Click for full size)
Here is a good description I clipped from the NASA Visible Earth web site:
In recent years, scientists have turned their attention to the ways in which human-produced aerosol pollution modifies clouds. One area that has drawn scientists. attention is "ship tracks," or clouds that form from the sulfate aerosols released by large ships. Although ships are not significant sources of pollution themselves, they do release enough sulfur dioxide in the exhaust from their smokestacks to modify overlying clouds. Specifically, the aerosol particles formed by the ship exhaust in the atmosphere cause the clouds to be more reflective, carry more water, and possibly inhibit them from precipitating. This is one example of how humans have been creating and modifying clouds for generations through the burning of fossil fuels.