The Appalachian Trail is marked by white blazes (rectangles) on trees or rocks or posts. Most are just single blazes.
If there is potential confusion ahead and you are supposed to go straight, you will see two blazes – one on top of the other – it usually means “pay attention “.
If the trail takes a sharp turn, there are two blazes but they are offset – you turn in the direction of the topmost blaze.
Since the blazes are white going northbound and white going southbound, it’s always a good idea to make sure I start the day headed north 🙂