In removing masking tape, stickers or adhesives from metal, glass, ceramic etc. Scrap with a safety blade or when the finish is important a fingernail, then wipe the area clean with lighter fluid such as Ronson or Zippo brand.
The fluid will evaporate quickly & leave the finish clean.
*Note do not use lighter fluid on non metallic painted surfaces, such as walls or woodwork as the fluid will take off paint as well.