An augury is a sign of things to come, like an omen. If you’re superstitious, you might think that seeing a black cat is an augury of bad luck.
The word augury used to refer to a way of predicting the future by watching birds fly. These days, if a flock of birds flies over your car, that could simply be an augury that your car is going to be, um, decorated. Not every augury is an ill omen, but usually an augury is a sign that the future will be none too rosy. Auguries are signs of what's to come, and it's wise not to ignore them.