For those of you who may missed this feature I wanted to point it out, because I think it is very powerful feature and the need for it increases every moment with number of topics and posts on the board growing. And I think it is not much widely used.
So basically you can use bookmarks to save topics (or even posts) for later reference.
List of your bookmarks is in your profile. Each bookmark can be removed from the list.
Add topic to bookmarks
Below each topic there is Bookmark button:
Add post to bookmarks
You can also bookmark single post. Below post click three dots and menu will expand so that you can see bookmarking icon: