When baking cakes, which of the following is a sign that the cake is done?

The indication that the cake is done is best represented by the clean toothpick test. When a toothpick is inserted into the center of a cake and comes out clean, it shows that the internal structure of the cake has set properly and that the batter has cooked all the way through. This method is widely utilized in baking as it provides a reliable measure of doneness beyond visual cues.

While a golden brown color and firm edges might suggest that the outer part of the cake is cooked, they do not necessarily assure that the inside has fully baked. Additionally, a sweet aroma, while indicative of the cake baking, does not provide any accurate measure of whether the cake is fully cooked throughout. Thus, the clean toothpick test serves as the most definitive sign that the cake is done.