The little blue seal with the checkmark (the "verified badge") indicates that this is a "verified identity" by Twitter: that is, Twitter asserts that this person has proved they are who they say they are.
Who gets to get verified? It's bit unclear. Twitter puts it this way: "An account may be verified if it is determined to be an account of public interest." Typically this includes accounts maintained by users in music, acting, fashion, government, politics, religion, journalism, media, sports, business, and other key interest areas. However, all members of Congress and senior administration officials qualify for such status. So do most major public figures and prominent writers.
If you don't see the blue badge, either disregard the tweet as suspicious, or do further research.
One additional note: sometimes people try to fake these indicators; an example is faking verification symbol in header. This user has used their background image to place verification badge next to their name. To steer clear of these sort of hacks, always view the badge in the sidebar or small ТhoverУ card, not the header, and to be extra sure it's legit, hover your cursor over it when you hover, the words Тverified accountУ should pop up.
- from Web Literacy for Student Fact Checkers by Mike Caulfield, https://mikecaulfield.files.wordpress.com/2017/01/webstrategiesforfact-c...