A content source provides metadata associated with content, such as an audio signal or video data, to a social networking system. The metadata identifies characteristics of the content or specifies an action for the social networking system to perform. A content identifier associated with the metadata is generated by the social networking system, and an association between the content identifier and the metadata is stored. The content identifier is provided to the content source, which encodes the content identifier into the content (e.g., as a watermark). When a client device receives the content encoded with the content identifier, the content identifier is extracted and communicated to the social networking system in connection with a user account associated with the client device. Based on the content identifier, the social networking system retrieves the corresponding metadata and performs an action in connection with the user account based on the metadata.