answered:
Use this code:
<a href=”URL OF NETWORK“><img src=”ICON IMAGE URL“>
For example: <a href=”http://the-tumblr-network.tumblr.com”><img src=“https://www.msu.edu/~frnclub/images/tumblr2.png”>
You can get the ‘icon image url’ by right-clicking on the image you want to use as the badge and selecting ‘copy image address’.
If you meant how to actually make the image for the icon, I would suggest getting a picture from google images and editing it, or making one in photoshop or you could use http://www.picmonkey.com. If you’ve created your own image, upload it into http://www.tumblr.com/themes/upload_static_file to get the image url x