A while ago, Gmail introduced a system whereby it uses “importance markers” to determine which messages are more important than others.
They can disrupt the look of your inbox though, and for that reason, some users may want to get rid of them.
To do so, head to the Gmail settings page, and then select the “inbox” tab at the top of the screen. Then, select the “no markers” option in the middle of the page.
Select “save changes”, and you’ll be done. The markers won’t show up anymore in the inbox.