My dictionary did mark it as Not US. I found the word in one of Ellis Peters's novels, and noted the passage, but have now lost my note, so I can't find the passage again. It comes via OE from Latin signum (which more recently gave us sign). Perhaps websafe or tsuwm could post the OED entry for us. The fact that Ellis Peters's detective, Brother Cadfael, is a herbalist inspired my poultice definition.

Bingley

Bingley