Is there a button you press as in the FreeBSD forums? I must be blind, I don't see it.

There's no button that reads "thanks" or anything like that. But there's a button in the upper right corner of any post that resembles a "thumbs up" graphic (next to the "quote" button). This is what you're looking for.

BTW: There's also a green "checked" icon there which can be used to mark a thread as "solved" (which is generally a good idea once an issue has been resolved).