Personal Level Indicators

How can I tell if a message was sent to just me or to a mailing list?

Gmail displays arrows, or 'personal level indicators,' next to messages in your inbox so you can tell if a message was addressed to you, a group, or a mailing list. A single arrow (>) appears next to a message when it is sent to you, and a group of others. Double arrows (>>) indicate that a message is addressed only to you. Arrows won't appear next to messages sent to a mailing list.

How to enable personal level indicators in Gmail 

1. Click the gear in the top-right  Select Settings.
2. Select Show indicators in the Personal level indicators

3. Section, and click Save Changes.

(If you'd like to disable personal level indicators, just select No indicators and click Save Changes.)
How to enable personal level indicators in Gmail - Video