iOS devices such as iPhones and iPad do not support HTML email signatures very well. Accurate display is difficult. However it is possible to do using a similiar method as with Gmail & Google Apps.
- Send yourself an email with your signature in it from a Desktop computer.
- Open the email that you sent to yourself on your iOS device. Select the area containing your signature and copy it to your iOS device’s clipboard.
- Open Settings > Mail > Signature (You may need to scroll down quite far to find it.)
- Paste your signature from your clipboard into the signature area.
If this instructions do not accurately reflect options or views you have available to you, your iOS device’s software may be out of date.
Bear in mind it’s impossible to get 100% accurate display using this method. If the results are not satisfactory you should use a plain text signature instead when emailing from your iOS device. Feel free to fill out this form on Apple's website to let Apple know you'd like HTML email signatures in iOS.