When you visit a website that uses SSL certification, most browsers will display a lock symbol in the URL bar to inform you that you're on a secure connection.
This may change soon as Google plans to flips this around. In a Chrome update anticipated to be rolled out soon, Google will start calling out HTTP websites as unsafe.
This means that websites that use the HTTP protocol, which is still the majority of websites, will receive a warning sign in Chrome' URL bar. Initiatives like Let's Encrypt are making it easier (and free) to switch to HTTPS, but it's not always easily implemented. Additionally, for less advanced users or users on shared webhosting it's still far from easy to obtain a SSL certificate.