How To Modify Your iPhone/iPad Signature
In order for your automatic signature to be properly applied to all outgoing messages it is necessary to force the mail application on iPhone/iPad to send the message using HTML. We can accomplish this by making a simple signature that is displayed using bold text, this forced the mail application to send the message using HTML. The following document will guide you on how to accomplish this on your device.
Begin by launching the settings application. once in the phone settings navigate down to the "Mail, Contacts, Calendars" click on its icon to enter it's settings screen. After entering the 'Mail,Contacts, Calendars" setting go down towards the bottom where you will find an option labeled "Signature" click on this item to enter the signaure options setting screen.
While in the signature settings you will see the text of your current iPhone/iPad signature it may say "Sent from my iPhone" you can leave this message or you can replace it with either a . or a -
Hold your finger over the text to select it. Once you have selected the . , - or the "Sent from my iPhone" text you will see a black bar popup with options to copy or cut the text, you will also see an arrow on the right side of this bar, click on this arrow to display additional options.
After having clicked the arrow you will be presented with a new option BIU click on this button to make the text of your signature "Bold" having this bold signature will force iPhone/iPad mail to send the message using HTML which will properly display your signature.
At this point you should now see that the text in your signature is bolded. You can now click "mail" in the top left of the screen to return to the settings menu, you can then exit the settings and test the signature by sending an email to yourself and seeing if the signature is properly displayed.