The folks at Twitter rarely update their Vine app for Windows Phone, but they have now done exactly that. The update changes the star icon to a heart for liking posts, which itself is a new label for favorites.
The new version number of Vine is 22.214.171.124. The change log that shows with the update is an old one from September, but going into the app itself does show the new hearts logo. Twitter explained their reasoning behind the change in a blog post, which also affects the official Twitter app for Windows 10.
Thank to Prasanna for the tip!