How to show a little arrow glyph after 'target="_blank"' anchors

What I wanted was a visual indication of which urls would open in a new window.

I found a pure css solution, that didn't require altering the html at all.

a[target="_blank"]:after {
	content: " \2197";

This means:

any `<a>` element with `target="_blank"`
 - should have a small "North East Arrow" after it.