I think he is referring to when he checks various threads the green triangle with a check mark is a thread that has a “ best answer” noted and the pin is a thread that is like one should pay particular attention to.
not sure if that is a thorough answer but perhaps there is a guide somewhere that someone can point him towards that explains in detail. Idk
Good catch, @Clove6060 . Exactly on the 'best solution' green triangle, so you might know to look at that thread if you have same problem to see an answer.
The pinned threads are "pinned" by Fitbit personnel to keep them at the top of section even when not active, as important information from Fitbit.
I can't think of any other such symbols.