So, I updated my test environment to the latest version and checked all the discussed things. Now I can say:
I will add a class to make custom icons the same size as the verification icon
In my fresh environment the custom icon will be displayed in profile and in posts. See this picture here:
Maybe another plugin removes several classes from the HTML markup. I will check if I can use another hook. Update: I looked for the icon in the posts. I use the class cAuthorPane_author to add these icons. Maybe the class is missing in your installation b/c of another plugin?