I've understood the meaning pretty quickly too, and I think it's a very nice gesture. If there isn't such a post (on the first 2-3 pages max) however, as has happened a few times, it's just a mystery death ribbon.
A few years ago, I saw a social media prank of posting a photo of an author - say, George RR Martin - with the caption "Renowned American fantasy George RR Martin at age 74, at his home in New Mexico yesterday. Martin's best known series, A Song of Ice and Fire was adapted into the television series A Game of Thrones."
but I guess it's also cultural... a black band for mourning it's a very eurocentric thing. I am not sure if it would make sense in other contexts. (but i really don't know)