Display Avatars in Posts for Mac With This Toggle
IPhone 6 (and 6 Plus) users get a handy little avatar in Messages so they always know who they’re talking to. Finer Things in Tech indicates that you can add the same avatar to Messages for Mac with a single switch.
In Messages, just click View> Show All Pictures of Friends in Conversations. Once you have done that, you will receive avatars in both group chats and single person conversations. This is a small tweak, but it makes it much easier to follow the conversation.
Messages for Mac: Display Avatars, Turn Off Alerts for Every Conversation | The finer things in technology