A new clue found within in the latest developer release of OS X 10.8 (Mountain Lion) suggests that 2012 may bring us the "summer of retina display Macs." A source with access to the latest Mountain Lion preview alerted Ars that double-sized graphics have popped up in some unexpected places, once again suggesting that Apple may be close to releasing MacBooks with high pixel-density screens.

One example comes from Messages, Apple's replacement for iChat. While using the app under the second developer preview of Mountain Lion, some icons are erroneously displaying 2x resolution art. In the image below, the "audio chat" icon is a 2x version instead of the standard 1x version, according to our source.

"I would interpret it to mean that Retina [MacBook] is close; perhaps concurrent with the release of OS X 10.8," our source said.

As we noted late last year, the tech to create suitably pixel-dense displays already exists, and the ability to adapt OS X's UI to those displays is already present in the form of "HiDPI" display modes. Apple has already been incorporating 2x UI elements such as cursors and other objects into recent releases of OS X 10.7 (Lion), as well.

With Mountain Lion scheduled to be released sometime this summer and Intel's next-generation Ivy Bridge processors expected to have wide availability at about the same time, we agree that this latest evidence points toward Apple unveiling MacBook Pros and possible MacBook Airs with "retina" displays in the next few months.