Example of how facebook have their warning in their console

facebook-warning.js

 const warningTitleCSS = 'color:red; font-size:60px; font-weight: bold; -webkit-text-stroke: 1px black;';
      const warningDescCSS = 'font-size: 18px;';
      console.log('%cStop!', warningTitleCSS);
      console.log("%cThis is a browser feature intended for developers. If someone told you to copy and paste something here to enable a Facebook feature or \"hack\" someone's account, it is a scam and will give them access to your Facebook account.", warningDescCSS);
      console.log('%cSee https://www.facebook.com/selfxss for more information.', warningDescCSS);