Hi Mike,
The best way to accomplish adding both your company logo and formatted text to your email signature in Method would be to use a mixture of some basic html and CSS code while entering this information. Here is a great link for learning some basics for html and CSS if you don't already know how to do this. Keep in mind for the logo, you should have your image uploaded to a specific URL that you will be able to reference in your html code, in my example, I used an image bank called imgur, where I uploaded the image to, and they provided me with a URL. Refer below to three useful screenshots I created to help with my example, and please let me know if this helps, or if you have further questions.
-Ben
Here is my signature field in Method:
Here is my Activity sending an email, adding the Mail.Merge Field:
Here is the final Email that was sent:
