You have to do that too. Well, you can never use their (the ISO) logo but you can use the logos provided by the certifying company to "prove" that you are certi

You have to do that too. Well, you can never use their (the ISO) logo but you can use the logos provided by the certifying company to "prove" that you are certified. People don't abuse those logos because the companies in question have a lot of lawyers and will litigate relentlessly.