The [S]
button in the image below is labeled as submitter
What does it do? I click on it but nothing happens.
I found this help page for "what is submitter reddit next to my name".
The [S] indicates that I'm the original poster, the one who started the page/link discussion, equivalent to having my name highlighted on Stack Exchange.
A comment of V2Blast:
In general, if you see an "S", "F", "M", "A", or "Δ" (delta), you can hover over it to see what it means.
(In order, those are "submitter", "friend" (you can add them as a friend from their userpage to more quickly recognize their posts), "moderator", "admin", and "admin emeritus" (former admin).)