rabbit's drawimageoverride does not work

act.doer should be passed to drawimageoverride instead of act.target, since rabbit's function is meant to measure sanity of the player, not of the sign:

function DrawingTool:GetImageToDraw(target)
    local ent = FindEntityToDraw(target, self.inst)
    if ent == nil then
        return
    end

    local atlas, bgimage, bgatlas
    local image = FunctionOrValue(ent.drawimageoverride, ent, target)

local function drawimageoverride(inst, viewer)
    return IsCrazyGuy(viewer) and "beard_monster"
end