Some Native American tribes believed that seeing an owl was an omen of death and others an omen of luck. Personally I think I am lucky when I get to see or hear such a majestic bird. It is just a bird in my opinion, no bad or good luck attached to it's presence, unless you count the fact that it is hunting rodents near your house, which is a good thing :D
I would consider it a bad luck since in our culture, owls are considered to be the bearers of bad news. However, in other cultures like the ancient Greek culture the owl was seen as a symbol of god fortune.