With the release of the current round of Disney Plus MCU shows, this seems like an appropriate time to remind everyone about the rules regarding spoilers. As writ, the rules call for a six month window where spoilers are kept concealed; plot developments should be kept out of titles, and properly obscured within bodies. The former is most critical, since it is much harder for someone avoiding spoilers to not catch view of a title while casually reading through the sub.
For spoilers related to "one and done" works (movies, single books, video games, one shot graphic novels, etc.) the date of public release is when the timer starts; films reaching theaters or streaming services, street date for games, and so on. For spoilers related to sequential works (series television, running comic books, books in a series, and so on) the release date for the specific episode/work sets the timer, while one for the work as a whole should go off the final release date. Using WandaVision as an example, the death of Maria Rambeau in the five years of the Blip was mentioned in an episode that came out January 29th, and in turn should be kept concealed until the end of July, while the complete absence of any known Avenger or any of the sorcerers of Kamar Taj from the events of the series isn't fully confirmed until the final episode released on March 5th, and wouldn't be fair game to bring up in the open until September. When in doubt, go with the release date of the final work in the series/franchise.
For putting spoilers in the body, the formatting for desktop uses "> !" (minus space) at the start and "! <" (minus space) at the end, with no spaces between the "!" and the text. It should look like this.
Finally, avoid "troll spoilers". False information designed and framed to look like a real spoiler (Snape was Dumbledore's sled, Rosebud was Keyser Soze all along, the butler did It, etc.) is not a violation of the spoiler rules, but it is a violation of the rules about not being a jerk and will prompt mod action.
UPDATE 27 APRIL 2021: Please keep in mind that revealing that something doesn't happen can be as much of a spoiler as saying something does happen. It's a spoiler for Falcon & The Winter Soldier to say the Dora Milaje show up with an axe to grind with Zemo for his role in the death of their King, but it's also a spoiler to say neither War Machine or Spider-Man show up to intervene in the Flag Smasher assault on the GRC meeting. Both types of spoiler should be obscured as noted above.