InDesign is not a tool for composing email signatures. You'd be wasting your time trying.
Ideally, the text of your email signature should be live text set using whatever signature feature your email client offers.
Generally speaking, I'd say adding a graphic to your email signature is a bad idea and somewhat inconsiderate toward recipients of your messages. Nevertheless for some reason, many people feel a need to do it, and one conservatively-sized graphic appears to be accepted as reasonable. On the other hand, sending "a few pictures" with every email would be rather bad form, in my opinion. If you can get it down to one polite visual embellishment, again using whatever signature feature your email client offers, simply paste it into the signature at the desired point.
Signature feature conventions vary among email clients, so you'd have to be more specific to get more specific guidance, but it's safe to say that attempting to compose a signature in an external application and get it into your email client will be an exercise in frustration and/or make a mess of your emails.
Thanks for your advice, I have since completed this task.