How to Use Text Formatting and Images in Apple Mail Signatures
To add colors, text formatting and images to a signature in Apple Mail:
Select Preferences under the Mail menu at the top of the screen. The keyboard shortcut is Command+, (comma). Go to the Signatures tab. Highlight the signature you want to edit. You have several options for formatting the text in the right window: To assign a font, select Format | Show Fonts from the menu and select the desired font. To assign a color, select Format | Show Colors from the menu and click the desired color. To make text bold, italic or underlined, select Format | Style from the menu, followed by the desired font style. To include an image with your signature, use Spotlight or Finder to locate the desired image, then drag and drop it to the desired location in the signature. Go to the Composing tab in the preferences window. Make sure Rich Text is selected under Message Format for formatting to be applied to signatures.
To assign a font, select Format | Show Fonts from the menu and select the desired font. To assign a color, select Format | Show Colors from the menu and click the desired color. To make text bold, italic or underlined, select Format | Style from the menu, followed by the desired font style. To include an image with your signature, use Spotlight or Finder to locate the desired image, then drag and drop it to the desired location in the signature.