Trigger:
Lua Code:
function() return IsResting() end
Untrigger:
Lua Code:
function() return not IsResting() end
Edit: I don't know if WeakAuras supports direct textures, but this is the data for the rest icon:
Texture: Interface\CharacterFrame\UI-StateIcon
Texcoords: 0, 0.5, 0, 0.421875
There's also an icon with "ZZZ", but it has a "x2" on it. WeakAuras has an icon box for this: 648642
This is what the icon looks like:
https://www.wowhead.com/icon=648642