Nope, not just signals....leave NO stone unturned! It's just that you get TWO chances to pass on everything else, the 1st and 2nd yard practicals (cuts/adds, preparing a train for service), the midterm, final, and road practical all give you two chances as far as I know.
However, the signals exam is the one that gets you terminated for ONE incorrect answer. Your TSS's will help you prepare, I had Richarson and Lovell...both EXCELLENT instructors!, It wasn't them, it was ME, I didn't get it done when I had the chance, and that happens to some of us. But for YOU, the advice would be to study them a minimum of 1hr a day, make index cards(paper AND app, I use StudyDroid), and of course classmates can quiz each other. The support system is there, and you can succeed where some of us didn't...You'll be alright, just go and get it!!