404. That’s an error.
The requested URL /bookmarks/mark?op=add&bkmk=http%3A//science.sciencemag.org/content/231/4745/1504.1&title=First%20Image%20from%20SPOT was not found on this server. That’s all we know.
/bookmarks/mark?op=add&bkmk=http%3A//science.sciencemag.org/content/231/4745/1504.1&title=First%20Image%20from%20SPOT