You can insert your signature at the current cursor location with the
command C-c C-s (mh-insert-signature).
By default, the text of your signature is taken from the file
~/.signature. You can read from other sources by changing the
option mh-signature-file-name. This file may contain a
vCard in which case an attachment is added with the vCard.
The option mh-signature-file-name may also be a symbol, in
which case that function is called. You may not want a signature
separator to be added for you; instead you may want to insert one
yourself. Options that you may find useful to do this include
mh-signature-separator (when inserting a signature separator)
and mh-signature-separator-regexp (for finding said separator).
The function mh-signature-separator-p, which reports t
if the buffer contains a separator, may be useful as well.
A signature separator ("-- ") will be added if the signature
block does not contain one and mh-signature-separator-flag is
on. It is not recommended that you change this option since various
mail user agents, including MH-E, use the separator to present the
signature differently, and to suppress the signature when replying or
yanking a letter into a draft.
The hook mh-insert-signature-hook is run after the signature is
inserted. Hook functions may access the actual name of the file or the
function used to insert the signature with
mh-signature-file-name.
The signature can also be inserted using Identities. See Identities.