It is possible to create an HTML signature for Mail on an iOS device without jailbreaking that device.
For this to work you need a backup of your iOS device made via iTunes.
First, create your HTML signature in your favorite text editor. It is essential that you replace the HTML tag delimiters < and > with the appropriate HTML entities: < and >.
Next, run Then run iBackupBot, choose your latest backup, then look for /Library/Preferences/com.apple.mobilemail.plist. Click on this file to display it in the editor, and find the section.
Below it you will find tags; paste your HTML code between these tags (overwriting what is already there) and save the file.
Exit iBackupBot, then restore your iOS device via iTunes. (Click on the device in the iTunes source list, then Option-click on the Restore button and select your backup.) The signature should then appear in any e-mails you send from that device.
Thx to Mac OS X Hints http://feeds.macosxhints.com/click.phdo?i=84d74ae82f7b0998f12471ac1660e9ce