Remove Paint from outdoor metal sill of Main Door
if this is an anodized aluminum sill (thats what it looks like), try using brake fluid.  it will destroy just about any paint bond out there.  just wipe up afterwards and degrease with a good quality degreaser.

be wary though, if its anything else other that anodized aluminum (or an other uncoated metal), the brake fluid will destroy the coating (even powdercoating will be toast)

if its vinyl, try cleaning it up with paint thinner and a toothbrush.  it may take some time but it usually works.  oven cleaners with sodium hydroxide in them also do a good job without damaging the vinyl.