Signature is a program which creates a dynamic signature file.  It does
this by creating a pipe to the fortune program, which, when read from,
prints out a random fortune.

To use, type

$ signature

This should return immediately.  However, signature is still working in
the background.  To stop the program, type

$ killall signature

You may specify an alternate filename on the command line.  The program
also understands the standard options --help and --version.