Unfortunately it is only possible to insert plain text into that field.
Thanks Neville, what a pity! I will have to email to myself first then send on to the customer
Otherwise print the quotation as a PDF file and attach it to your email.
I'd have no idea, but that radio button says "use html". As long as the mime type in the email is set to html then any html code should work. Try sticking this in that box and see if it does anything?
Replace the url with a valid image to test, if it works then just upload your actual graphical signature to your site somewhere.