Hi @ctsygiel,
Let’s Encrypt offers domain validation (DV) certificates, which do not assert the identity of the person or organization that runs a web site. There are other kinds of validation that we don’t offer, such as extended validation (EV). You might be hearing about the difference in the way that browsers visually show the presence of each kind of certificate.
Every browser shows this graphically in a slightly different way, and older versions may be different from current versions. A simple way to describe the difference in visual indication is that many current browsers show a green padlock with DV and additionally show a green bar (with site operator information) with EV.
If you want to see how a particular browser will display the presence of a Let’s Encrypt cert, you can visit https://helloworld.letsencrypt.org/ in that browser and see what it will look like. To contrast that with how the browser displays the presence of an EV cert, you could visit the certificate authority https://www.globalsign.com/ (which issues EV certs itself and also uses one on its home page). You might, for example, see a green bar with the GlobalSign cert that you won’t see with the Let’s Encrypt cert.