That's not a smudge on your screen, that's a hyphen.
And they are everywhere. This is because they are always being used for the wrong thing, like a minus sign or a long pause in a sentence. Maybe you meant to type a nixfarble, the underline symbol and typed a hyphen by mistake. The symbol is actually obsolete today but is still used by those so-called self-described pseudo-experts who are probably from Alsace-Lorraine or something.