There are two different kinds of spoilers.

glennmagusharvey

1. "true" spoilers: These spoilers will spoil the experience for people who are completely new to it.  Example: Picture of recently-deceased Aeris in the Temple of the Ancients.

2. "dog-whistle" spoilers: These spoilers will only spoil the experience for people who have some information about it.  Example: fanart featuring various gruesome things done to Madoka characters, among which is headless Mami (highlight to view).

Note that, sometimes, labeling something as a spoiler provides information to people who were previously newbies, which allows them to understand that it is a dog-whistle spoiler.  For example, if you tell me that that second example is a spoiler (as people have), I will suddenly come to actually expect that in the show.  If you don't, I would continue to think that that's just some crazy fanart.

Note that this really is situational; the broader the scope, the more you can say something is a dog-whistle spoiler rather than a true spoiler.  For example, if you've never heard of the Final Fantasy games, my talking about Aeris and the Temple of the Ancients would be meaningless to you.  (That said, you might make a minor mental note of it if you DO ever encounter a character named Aeris.)

Discuss.

Dog-whistle spoilers be skillfully used to avoid using spoiler tags?  I have a meatspace friend who's voiced objection to the use of spoiler tags because he feels it breaks up the flow of reading.

Saigyouji

Except the latter has multiple pieces of fanart. Are you just going to assume, "oh hey, this must be a weird fan meme!"?

Icalasari

Dammit I thought this was going to talk about highlight spoilers vs spoiler boxes

glennmagusharvey

Are you just going to assume, "oh hey, this must be a weird fan meme!"?

Definitely ain't the first time that's happened.

ClockworkUniverse

If trying to avoid spoilers for something, viewing lots of fanart for it isn't very smart.

glennmagusharvey

Well, this goes back to my trying to tell people that they shouldn't have identified headless Mami in Madoka as a spoiler, because when I ran across that one fanart piece on Youtube, I wouldn't have thought twice about it, had people not made a big deal about it.