there is no "verified" label on mastodon (the people who seem to have one just use a custom emoji). _but_ that doesn't mean there's no way to prove your account is actually yours.
if you have a website, you can put a link of the following format on it:
<a rel="me" href="(link to your mastodon profile page)">...</a>
this link can be anywhere on the website's index page.
if you do this and then set one of the "profile metadata" fields to link to that website, mastodon will see the link back to your profile page and show that link as "verified" by coloring it green and adding a checkmark.
for example, my profile has a verified link to my website.