You're at best a third part contractor doing promotional and advertising services for another company. Of course, the laws will be different around the world so what would happen would be different depending on jurisdiction but there's little chance you would personally be in trouble, but maybe your country has different laws on what people are allowed to advertise. I'm sure you could potentially get into trouble for advertising illegal services but I would be very surprised if someone came after you or other people who were advertising a company on some random website. How would they even know who you are? It's not like you've signed a contract with them and they have all your details that law enforcement can get if they shut down a service. All they have is a username on a forum unless they subpoena the board to get more information but I doubt that would happen just to try find out who was advertising them here. With that being said, if you're worried about something then I would err on the side of caution.