A smiley face in the footer on twenty twelve – is that normal?

That’s the marker used by wordpress.com stats (or the Jetpack version). It doesn’t normally display if you’re logged in, but can normally seen by visitors.

Nothing to be alarmed about.

I’ve seen that on a few 2012 themes tbf.

it is actually styled in style.css (line 1410) of Twenty Twelve:

/* =Plugins
----------------------------------------------- */

img#wpstats {
	display: block;
	margin: 0 auto 24px;
	margin: 0 auto 1.714285714rem;
}

change to ‘display: none;‘ if you want ot hide the smiley.