How to Detect Witches

Early in the morning, on the first Monday of each of the four quarters of the year, the smoke from a witch's house goes against the wind. This may be seen by any one who takes the trouble of rising early and going to an eminence, whence the witch's house can be seen.   (Witchcraft and Second Sight in the Highlands & Islands of Scotland, J.G. Campbell)

Just in case you're trying to find some witches. They can be tricky to locate these days.