Liking something via Facebook is a popular activity with consumers and a productive promotional tool for retailers. If a consumer Likes a product on a retailer’s e-commerce site, that Like and information about the product is transmitted to her Facebook page where her myriad friends can take note.

Facebook today has brought the Like functionality for web sites to the realm of mobile apps, releasing Built-in Like, a tool app developers can use to incorporate Like buttons on products and content within an app, including mobile commerce apps.

“The new Built-in Like action makes it easier for people to share content from your app,” writes Facebook’s Andrew Rothbart in the social network’s official developer’s blog. “While the Like button is a great way to let friends share content from the web back to Facebook, the Like action enables you to build your own Like buttons for your mobile or web app and drive distribution across Facebook.”

Instagram and foursquare have implemented the new mobile Like functionality in their apps. On Instagram, for example, when a person Likes a picture a Facebook friend has posted, that friend gets a notification and the photo Like is posted on the person’s Facebook page.

Facebook stipulates that a Like may only be published when a person performs a Like action. For example, if someone gives a movie a five-star rating in a movie app, that warrants a rated action rather than a Like action, Rothbart writes. For more information on rules for using the Like button, he directs developers to consult Facebook’s branding guidelines.