Prefixes for official, spoiler, and NSFW topics have been added as a function on the forums for all members (except for the official one). To use them, when creating a topic, select the appropriate prefix from the drop down that is above the Subject line.
Note: while the rules haven't been updated, members seen abusing these prefixes and attaching them to topics that they do not apply to will be warned and/or banned. Use them as they were designed, please.
kthxbai