If the problem only occurs with Secure Boot enabled, then it very much *does* look like a signature problem. But I'm not really a big expert on what the OS might be happy or unhappy with. This is also not really a problem that is specific to madCodeHook. You would probably have the same problem with any other driver, too.
I wish I knew how to solve this problem, but I really don't. I don't really have any more information about this than you have. I think your best bet is to contact either Microsoft or your certificate provider, and ask them why the OS doesn't like the driver.
If you want to double check if the problem is specific to the madCodeHook driver or not, you can try one of the many CodeProject projects which deal with drivers, e.g. a quick google search showed me these:
https://www.codeproject.com/Articles/60 ... ce-Drivershttps://www.codeproject.com/Articles/20 ... -executionWhat I can say is that there are a couple of madCodeHook users who I know have it working with Secure Boot enabled. So it seems unlikely to me that it could be a madCodeHook specific problem.