When you have iPhone there will be lot more you can do it. You might be sending emails through it to your friends, family, organizations friends and everyone one including officials. The default signature stamp in iPhone is Sent from my iPhone and you can change it any text you desired including HTML.
You can create HTML iPhone signatures easily via CoolGeex.com an application developed to generate HTML iPhone signatures. Here the signature can be directly create from your iPhone or from your computer or laptop.
The link is iPhone Signature Creator version 3
In that above form please make sure that you enter required details like email address, name, phone number and residential address as most of the information asked there is optional and can be skipped like Complimentary Close, first name, last name etc.,. You can even make your Title and Company boxed have turned into colors, either bold or italic.
Apart from that you have options to provide your own customized logo image supporting JPEG, GIF format images and the landing page on the logo.
Also if you like you can show FaceTime Link, Twitter Icon, Facebook Icon, LinkedIn Icon in the email signature.
And finally you require PIN number for the first time when you are using it, you need to generate it here.
And finally your email signature is created and you need to navigate to site listed below in the image on your iPhone.
There you need to provide the PIN number and it will then display the custom choosed HTML signature. The next step is to copy it and paste it into signature by navigating to Settings > Mail > Signature (Sent from iPhone).