The maple syrup will initially look glossy, even when it starts to bubble. It looks like melting plastic with a bit of a sheen. Once the syrup crystallizes it will no longer be clear and smooth because the structure of the sugar has changed. It will become grittier, like granulated sugar. It will be stiff and more difficult to stir the almonds and the coating will begin to form around the outside of the almonds and stick there. Even when it crystalizes and dries, the coating will not be hard (as it would be when you make candied nuts with granulated sugar) but it will have adhered to the almonds nicely.