Host an image
Your own branding/logo can be applied when you purchase signatures.
Simply find the image you like, right-click it, and choose "Copy image address"
However if you don't have a website, or want to use a different image than what's available on your website, you can take advantage of Google Drive Drawings:
Create a DRAWING
Create your drawing
Use the functions like shapes, text, and upload to make your image.
Tip: If using Upload to bring in an existing image, ensure the file you're using is PNG format.
JPEG isn't appropriate as they just appear black in the next step