apotropaic marks before, and mentioned the ones at the Tithe Barn in Bradford-on-Avon. Here are some pictures of them; they are daisy-wheels inscribed with a pair of compasses or dividers, probably by one of the masons who built the barn. Exactly what symbolism he may have intended is unclear (the daisy-wheel is a symbol in Heathenry, but it is very unlikely that he was a Heathen). The Tithe Barn was built in the early 14th century as part of the medieval farmstead belonging to Shaftesbury Abbey.
Anyway, the marks are a very clear example of the type. I took these photos on my mobile phone last Sunday.