Biggest question you still have overall

What is the one mystery or question you have about the series overall that you hope we eventually end up getting answers to? I for one would be kind of disappointed if we don’t get any explanation or backstory on how the symbol came to be and what it could possibly mean. It has been such a key part of the show this far it would be a little lame for there to be no pay off in that sense in my opinion. And obviously how they are eventually rescued is another big one, but I assume that’s a mystery we will get obvious answers to at some point in time. I also want a clear answer on who sent the damn postcards. I know it’s been heavily debated but I am firmly in the camp that they were NOT sent by Jeff, it has never been 100% confirmed either way. Thoughts?