I don’t remember exactly what the code is, but if you search “image bb code” and then put the URL of your image in the bb code provided that should work.
Hmm, can you directly reference a google drive item in a signature? I am not so sure you can,
When I clicked you link it put me in a viewer. I clicked show me the image in another tab and it gave me this
I think you need to put it on a photo sharing site like google photos (https://photos.google.com/)
Then you can include that in the signature using the bb codes.
Flickr is another very popular site but since yo already have google credentials then Google Photos would be the trick (formerly Google Picasa)
I use imgur.
Make an account and upload the image.
Then put the link to the image in the brackets.
As you can see, it works for me.
same I use imgur and 600 px wide is good
Create a permalink, for example,
Michael’s image becomes http://gdurl.com/7ysz