Ready for Burning Crusade, Classic, and Shadowlands!

DejaDonate:

DejaAutoMark will automatically place a Circle on tanks and a Moon on healers when in a non raid party. You can also disable automatic marking and use a slash command or keybinding to mark the tank and healer on demand!

Why Circle and Moon?

Circle is the next to last mark used with DBM and BigWigs and is thus less likely to be overwritten by their procedural marking code. While Star is last in their series it is more commonly used by players as a target marker.
Moon references Elune, the moon godess of the Night Elves and healing. Moon also offers the most contrast of color over distance compared to Circle which makes distinguishing which mark is the tank and which is the healer much easier.

DejaAutoMark's keybinding is located in the Keybindings menu under "AddOns"

Slash Commands:

/dam Shows the DejaAutoMark slash commands.
/dam on: Enables DejaAutoMark automatic mode.
/dam off: Disables DejaAutoMark automatic mode.
/dam mark: Marks the targets regardless of automatic mode status.