By adding the following line to your vimrc, you can use a simple email signature rotator:
map <Leader>ms :e c:\sign.txt<CR>ggV/^-- $<CR>k"*xG$a<C-R><C-O>*<Esc>:w<CR>:bd<CR>G$a<C-M><Esc>"*P
This rotator expects the user to have a file at the location C:/sign.txt with the following information:
-- first signature -- second signature -- third signature --
When a user finishes an email, they may call the shortcut \ms and the 'first signature' will be inserted into the email. This will also push the first signature in C:\sign.txt to the end of the file. To change to a different signature from the one which is next in the file type u and \ms again.
The sign.txt file must employ a signature separator like the following: '-- '.