By enabling Gmail’s Personal Level Indicators feature, your emails will be marked at the subject line, like this:
( › ) Messages sent to you and a group of others
( » ) Messages sent only to you.
No arrows next to message indicates sent to a mailing list.
Set it up like this:
While in Gmail, at the top of the page to the extreme right, click on the Options icon to the right of your name. Click on MAIL SETTINGS. Scroll down and enable “Personal level indicators”. At the bottom of the page, click SAVE SETTINGS.