The example is from Rochias (Swiss, 18th century). It appears in others too (not always so clear, due to stencilling: differing colours & going across lines etc).
Possibly and probably it is just an artifact of the woodcutting and stenciling process. To be clear, I am not claiming that there is any intentional esoteric or hidden meaning. Just that it is sort of 'neat', and from an artists POV at least, interesting. And of course, such even if an accident can have DM significance, whether intentional or not.