I think it's pretty well established that crop circles are made by people rather than aliens. However, when done right they are an awesome sight.
Looks cool...but yeah they're man made. If you are looking for creative ways to advertise, write your website name in the crops lol
Imagine if you were an alien, and you just traveled a several trillion miles to get here (there's ~5.8 trillion miles in a single light year), and it probably took you many years even travelling the speed of light. Do you really think they would be like, "Oh damn... let's make designs in crops and go home!"?