Type...                 In order to...
=======                 ==============
cd                      Change to your home directory (i.e., $HOME or ~)

pico .signature         Use the pico editor to create a .signature file.
                        (Replace "pico" with another editor if you like.)

<your signature>        Note that most systems require your sig to be <= 4
                        lines.  And it's good netiquette to make it as
                        short as possible.

<save and exit>         In Pico use ^x to exit and answer y when asked
                        if you want to save your changes.

chmod 644 .signature    Make .signature readable by all.

chmod a+x .             Make home directory searchable by all.