Simple rule: Is it related to the stream? If no: it can't be posted. If yes: Is it NSFW? If no: It can be posted. If yes: Can it reasonably be made SFW? If no: is the NSFW reasonable: If yes: it will be marked NSFW. If it is unreasonable: It can't be posted. If it can be made SFW: They need to clean it up.