Hey All! I do not know the best way to post this but I wanted to share my experience trying to fix an email signature in case someone else runs into the same problem.
I have an HTML signature that I have saved in Outlook and it can be easily copy/pasted into Word or other HTML friendly places without any modification.
But! When I paste it into the Dynamics 365 Signature window, it looks like this!
So, here is what I did to fix it. I created a new email within Dynamics 365, inserted the signature and checked the image properties (right click the broken image icon)
At this point, it was pretty clear the the URL for my images was changed somewhere along the line. However, the Alternative Text field stores it perfectly.
Copy the Alternative Text field and replace the URL field with it. You will see the image load as soon as you click off of that field.
Do that for all of the images in your signature.
Once you are done, select your entire signature and copy in (right click or CTRL + C). Then open your signature editor and Paste this version in there.
The signature loads the images correctly. Using the built in Dynamics 365 Email Window seems to resolve whatever the issue is.
I have no idea why this happens but this worked for me and helpfully will save someone else some grief!