RaidMobMarkerHUD is a standalone addon of RaidMobMarker.
The HUD provides a circular window for one-click marking. To display it, use the assigned key (see WoW's keybinding options) or the slash command.
To mark a target with a raid symbol, target the unit, hold down the assigned button or hold down the assigned button and target a unit.
Left-click a symbol and your current target will be marked with it. To unmark the current target simply right-click on a symbol. While holding down the button, the HUD will re-show when you change your target.
/rmmhud show shows/hides the HUD (for use with macros)