With 8.5x, Lotus added the ability to create, edit, and store your richt text signature in your mail preferences.
Next up: Allow us to set default font, size, color, and background for emails AND have different options for replies - some folks really really like to have the replies in discernably different color/font. Blue is a fav, for some reason.
Personally, I like Georgia, 11pt, black. It get's tiring have to either change every email, or change my template - and if I do that means I'm running an OFFICIALLY unsupported template.