A lot of websites become responsive to mobile devices these days, and there are a lot of different implementations. One I’ve seen is with the use of the Hamburger Menu, that symbolizes a folded menu. Some websites use special made fonts, like genericons, and others use a simple image.
But there’s another option: the HTML Entity IDENTICAL TO (≡ or ≡ in decimal). It’s almost the same and you can tweak the size with font-size.