The invention provides a high-visibility roof-drain cover comprising a roof-drain cover, a marked, reversible, elongated flag, and coupler means for mounting the flag to the roof-drain cover, wherein the flag extends upwardly from the roof-drain cover a sufficient distance that a top portion of the flag will remain visible above an accumulation of wind-blown debris and snow. The invention provides a first group of high-visibility roof-drain cover embodiments, each of which includes a novel roof-drain cover. The invention provides a second group of high-visibility roof-drain cover embodiments for retrofit, each of which includes a prior art roof-drain cover. The invention provides a third group of sub-assemblies for retrofit.