All hotels reserve the right to inspect your room whenever they need to. The privacy sign just means you don’t want room service, it’s not some magical lock.
They’d still knock, not just burst into your room to catch you in flagrante.
That said seeing the black hat conference in this way is daft.
This is an attempt to stay within working time regulations in the UK but they are violating this bit
By having a 19 day unbroken run which, as I understand it, is not legal.