In the context of Quatro Plus, a quality label, also known as a trustmark or seal of approval, is a claim by an individual or organisation that a website meets a defined set of criteria. For example:
Web Mèdica Acreditada reviews websites that offer medical information and gives a seal of approval to sites that meet standards of medical accuracy and publishing quality. Users searching for information about medical matters can have greater confidence in what they read knowing that it has been reviewed by qualified medical practitioners.

Although the domain of expertise varies, the same basic model is true of all trustmarks: in Britain, the Interactive Media in Retail Group (IMRG) runs the Internet Shopping is Safe trustmark; Thuiswinkel is a similar scheme in the Netherlands.

In these cases, and many more like them, a fee is charged to audit a website (and associated procedures) to ensure compliance with the stated criteria. This is generally done annually but more frequent checks can be made if new content is added or existing content changed, for example. If a user clicks on a WMA label, the award date and the last time the label was reviewed will be displayed. This information is fetched from WMA's database.

Perhaps less obvious in this context are schemes such as the European Blue Flag accreditation scheme for beaches. Among the many thousands of beaches listed on their website are several on the Gulf of Genoa. The local municipality (Commune di Spotorno) presents information on the Blue Flag scheme on their website.

Members of professional organisations like to display their qualifications too. For example this Czech plumber works to an ISO standard that, in exactly the same way as the WMA case, provides users with information that the work offered conforms to an independent standard.

All these are examples of Quality labels and the organisations or standards bodies behind them are referred to within Quatro Plus as Labelling Authorities.