These instructions assume that you have an HTML file that contains the email signature you wish to install.

1. Open the html file in Safari (not another browser), use the command Command-A to select and Command-C to copy the design to the clipboard.
2. Send yourself an email message from your computer, and in the body of the email, paste the email signature with Command-V. Make sure you can receive this email message on your iPhone or iPad (you will copy-paste it from the email).
3. Open the email in the Mail app on your iPhone or iPad.
4. Press and hold down on the signature in order to bring up the selection tool. Move the anchors so you have the entire signature highlighted.
5. Tap on Copy.
6. Press the Home button to return to your Home screen.
7. Launch the Settings app.
8. Tap on Mail, Contacts, Calendars.
9. Tap on Signature under the Mail section.
10. Tap on the account you'd like to add the signature to if you have signatures set up per account.
11. Tap in the signature field to bring up the selection tool again.
12. Tap Paste in the popup menu.
13. Shake your iPhone and tap Undo in order to remove any automatic formatting iOS may have done. This will bring back any colors or other HTML content that may not have shown up in the original paste.