This is an obelus:
The obelus was originally used to highlight dodgy bits of a manuscript, especially the parts that were suspected of being by someone other than the original writer. It was invented to mark bits of Homer, but later it was used to flag bits of the Gospels.
Nowadays we usually come across this sign in maths, where it means division...
...unless you're in Norway, where they still use the obelus sign ÷ in its old meaning of minus.
Yes, I thought aaarrrggghhh when I found that out, too,
Thing To Use Today: an obelus. This sign was invented by a guy called Aristarchus to mark dodgy bits of Homer, but by 1659 it was being used to mean division (except, as we've seen, in Norway, and, until quite recently, in Denmark). The word obelus comes from the Greek word obelos, the sharp end of a lance.