How will Amazon deliver packages by drone in tricky places? A new patent offers a clue.

Every once in a while, Amazon.com Inc. (NASDAQ: AMZN) lets the world know what it might be planning — not in a public announcement but in a patent filing. The company has filed thousands of applications since its founding, and while many don't go anywhere, some go on to disrupt long-existing industries. This week, the U.S. Patent and Trademark Office issued about 50 patents to the company, many of which Amazon applied for a years ago.