With iOS 6, you can now add different signatures for different e-mail accounts, but you can also add logos, links and styled text.
If you have an HTML or styled signature in Mail on OS X, do the following:
1. Send an e-mail to your account with the signature from OS X.
2. Open the e-mail on your iOS device, then tap and hold the signature text.
3. Select all the text and images of your signature, and then copy it.
4. Go to Settings > Mail, contacts and Calendars > Signature. In the text field, tap and hold again to display the Paste menu and paste your signature.
Only styled text (bold, italic or underlined), plus images and links will be copied. Text colors or font sizes will not.
[kirkmc adds: We had a hint giving a much more complex way of doing this back in April. This is very easy to do, requires no third-party software or futzing around with backups. Though, to be fair, think carefully if you really need images and logos in your e-mail signature…]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20121030204258477