[Ailae]

I'll give a drycode try (meaning I didn't try it ingame). :P

aggrodisplay.xml

<Ui xmlns="http://www.blizzard.com/wow/ui/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.blizzard.com/wow/ui/">
<Script file="aggrodisplay.lua" />
 
    <Frame name="aggroFrame" parent="UIParent" toplevel="true" movable="true" enableMouse="true">
        <Size x="76" y="30" />
        <Anchors>
            <Anchor point="TOPLEFT">
            </Anchor>
        </Anchors>
        <Scripts>
            <OnMouseDown>self:StartMoving();</OnMouseDown> 
            <OnMouseUp>self:StopMovingOrSizing();</OnMouseUp> 
            <OnLoad>aggroFrame_OnLoad(self);</OnLoad>
            <OnEvent>aggroFrame_OnEvent(self, event, ...);</OnEvent>
        </Scripts>
 
        <Layers>
            <Layer>
                <FontString name="aggro" inherits="GameFontNormalSmall" font="Fonts\ARIALN.TTF" text="*" justifyH="RIGHT">
                    <FontHeight>
                        <AbsValue val="26"/> -- text size
                    </FontHeight>
                    <Size x="76" y="30" />
                </FontString>
                                    
            </Layer>
        </Layers>
    </Frame>
 
</Ui>

aggrodisplay.lua

function aggroFrame_OnEvent(self, event, ...)
    local aggro_TRUE = "Aggro !";
    local aggro_FALSE = "*";
 
    if (event == "PLAYER_REGEN_DISABLED") then
        aggro_TRUE = "Aggro !";
 
        aggro:SetText(aggro_TRUE);
    end
 
    if (event == "PLAYER_REGEN_ENABLED") then
        aggro_FALSE = "*";
    
        aggro:SetText(aggro_FALSE);
    end
 
end
 
function aggroFrame_OnLoad(self)
    self:RegisterEvent("PLAYER_REGEN_DISABLED");
    self:RegisterEvent("PLAYER_REGEN_ENABLED")
    DEFAULT_CHAT_FRAME:AddMessage("Aggro Display loaded -OK-");
end