Is registering on a forum that contains songs and indecent clips considered cooperation in sin and transgression?

Singing and watching indecent clips are forbidden, as is any participation in or assistance with such activities. This is based on the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah; indeed, Allah is severe in penalty" (Al-Ma'idah: 2).

Therefore, registering in a forum as described is considered cooperation in sin and aggression and is not permissible.