Can I place a picture in the email signature on an iPad Air?
You cannot put an image in your signature on iOS. If you use Macmaniman's strategy of pasting in an image, the image will show up in settings, but not in an email. (tested on iOS 7)

A workaround is to insert the company logo into each email as you are writing it. However, I don't see why you would want to do this. It's a lot of work and your recipients will probably be annoyed because your images are wasting space in their mail account.