It requires the code modification. You should create methods which will detect the available membership type and then add the icon into the needed column.
P.S. It's possible to add the image into the language value. But in this case, this icon will show up everywhere the membership value is used and if you use the Role label on avatar for the membership, the added image will also appears on the avatar.

By 'create methods' we meant the custom code development. To see how this or that method/function works in Oxwall, you can download the Skeleton Plugin: http://www.oxwall.org/store/item/695/ Also, you can check out the Oxwall Crash Course: https://docs.oxwall.org/dev:crash-course

If you feel you can't handle this modification, we suggest that you search for the third-party developer who can assist you with it.