Vim swap files begin with the magic string
b0VIM followed by a space and the Vim version number. An empty swap file is not normal and may indicate a more serious problem.
Note that the
ATTENTION message exists partly to warn you when another Vim process is editing the same file, so you may want to keep it even for cases where you know there are no pending changes. The warning tells you whether the file is modified and whether the previous process is still running: If neither, it should be safe to delete the swap file, otherwise you should proceed with caution.
You can disable the
ATTENTION message with
set shortmess+=A, but Vim does not expose enough information about recovery in the API to disable the message automatically in low-risk situations. If you're very careful about workflow, you could disable the message and then deal with recovery manually as necessary. If you take this approach, you may want to streamline swap file processing like this: http://stackoverflow.com/questions/63104/smarter-vim-recovery