From the forum guildlines thread:
Talking about what happened in the latest episode, no tags needed. Talking about stuff from the book that has not happened yet, use spoiler tags. Or just don't post I guess. Your choice.9. Spoilers If you have information from say a book (Or any other source) a movie or TV show is being adapted from you need to use spoiler tags. Same thing if you have found reliable leaks online. Do not ruin other's excitement when we have a system in place to deal with this. Otherwise spoiler tags are not required, regardless of how a topic is titled. You should be able to discuss the most recent events that have aired or been released without needing to use spoiler tags. If you want to discuss spoilers, use the tags.