"Ed nailed it. And even if, as Karol pointed out with his photo, that an old logo appeared in a 2015 book, that assumes a designer can rifle through every source before settling on an idea. Even if a designer were to check their ideas against the Patent and Trademark Office database, there's no guarantee that every image is in the database. There are only so many ways to skin a cat. And when you design a logo, you come across visual pathways that just seem natural or obvious. The AirBnB logo is the most arguably egregious, but even then, when you work with a capital A, you're going to figure out how to make the crossbar or the suggestion of a cross bar. Maybe it's a twig, maybe it's not there at all, maybe it's a dot. You want to do something that gives an A its essential A-ness. A little loop was probably one of hundreds of A sketches. It's overall roundness suggests comfort (read: pillow), something you're going for when you are deciding where to put your head at night.A logo based on the first letter of a company name is actually a very smart solution. It's not, as Sean suggests, an easy way out at all. It becomes an emblem of sorts, giving a company a lot of flexibility for merchandise or for use as a repeating graphic element.Designers, at least this one, live in fear of duplicating someone else's design. It's quite hard to do something entirely original. The best you can do is make the details unique: line weight and style, color, font, scale of elements, etc."