A few weeks ago, Facebook started publicly testing a gifting program around its virtual currency, “Facebook credits”. In the test, users were able to give each other Facebook credits as public reward for content they posted to their stream – a kind of “Super” Like. Now, Facebook has expanded its virtual currency gifting experiment to branded virtual gifts in a test that’s currently running with Mars.

Here’s how it works: When fans go to a Facebook Page of a Mars candy bar like Snickers, Twix, or Milky Way, Facebook has installed a special version of the Gifts application on the Gifts tab. In this version, the branded virtual gifts (in this case, a virtual candy bar) also come bundled with 10 Facebook credits.

In other words, Facebook is enhancing the virtual gift with a virtual gift certificate (worth about one tenth of a standard Facebook Gift) to the Facebook Gifts store.

By this point, it’s clear that Facebook has broader ambitions for its virtual currency than simply directly selling items from the Facebook Gifts store. The company is hoping to broaden the utility of its currency by more deeply integrating it into the social actions already happening on the site. For example, rewarding a status update or interesting photo.

For advertisers, this means Facebook is working hard at trying new things to increase the volume of branded virtual gifts sent through the Facebook system. Branded virtual gifts are one of the more promising new forms of online advertising in social environments, because studies show they’re often a form of advertising that people actually like to receive.

Whether or not Facebook integrates its virtual currency with applications on the Facebook Platform, Facebook credits are quickly becoming an increasingly visible part of Facebook’s monetization strategy. Branded virtual gifts are likely to become  a mainstay part of its direct sales efforts, but there’s no reason why Facebook couldn’t expand the program to more advertisers in the future.

This particular campaign is part of the “Mars Real Chocolate Relief Act” and Free Chocolate Fridays: every Friday from now until September, Mars will be mailing out 250,000 coupons that you can redeem for full-size packages of chocolate that you can get from its website Realchocolate.com.