You should always create and use a signature on all of your outgoing e-mail messages.  You can have separate e-mail signatures for each account on your iPhone/iPad. This can be helpful if you have a business and personal e-mail account and you want the signatures to be different. This process is shown using iPhone, but works the same on iPad.

The easies way to start is by sending yourself an email that ONLY contains your signature (including a logo if desired):

1.   Open e-mail you sent to yourself.
2.   Press and hold over any text in your signature.
3.   Tap “Select All”.
4. Tap “Copy”.
5. Tap Home Button to return to Home Screen.
6.   Tap “Settings” icon.
7.   Scroll down and tap “Mail” (this is now separate from Contacts and Calendars in iOS 10).
8. Scroll down and tap “Signature”.
9.   Tap “Per Account”.
10. If there is existing text, tap and hold inside text field.
11. Tap “Select All”.
12. Tap backspace key to erase (after all text is highlighted).
13. Tap and hold in blank signature field.
14. Tap “Paste”.

*If the signature you pasted contained colored text, you can SHAKE your iPhone and tap “Undo” to “change attributes”.  This will restore the signature to the original colors you copied from the e-mail you sent to yourself.