Even if you can peel most of the paper off a sticker stuck to metal, getting those last stubborn bits of adhesive off without scratching the metal may cause a conundrum. Use citrus-based solvents, a plastic scraper or even a hair dryer to help remove the remnants of the sticker and its adhesive.
Pick at a corner or edge of the sticker until it starts to peel; you may have to try different areas to find a part that easily can be peeled up. Jam a thin plastic scraper under parts that lift up to make the process easier. If the sticker leaves behind a thin layer of paper or adhesive residue, rub your fingers, a dry washcloth or a nylon non-scratch scrub pad over it to loosen more of the paper and the adhesive beneath it.
Citrus solvents designed to remove sticky messes from many surfaces do the job well when it comes to removing stickers from metal.
Squirt a few drops of the solvent on the sticker or sticker residue, using just enough to moisten whatever is left of the sticker. If the sticker is on a vertical metal surface, apply the solvent to a cotton swab or paper towel, rubbing the solvent over the problem area.; otherwise, the citrus liquid may run or drip.
Wait several minutes, then rub away the residue with a soft cloth or a folded paper towel, or use a plastic scraper.
Wipe the area again with a dry cloth to remove remaining solvent. If the area still feels oily, wipe it down with water or vinegar, drying the metal with a soft cloth or paper towels afterward.
Wet sticker remnants with rubbing alcohol, inexpensive vodka or equal parts white vinegar and water, allowing the sticker to soak up the moisture for a few minutes. All of these materials help dissolve the glue or make it lose its stickiness, which makes the sticker gunk easier to remove with a plastic scraper.
Help From a Hair Dryer
If the sticker is so stubborn you can't peel it up at all, heat it with a hair dryer on high heat. Warm one end of the sticker at a time so you can pry up one of the edges. The heat softens the glue, making the sticker easier to lift. Continue heating the sticker with the hair dryer held 4 or 5 inches from the sticker. Keep your other hand out of the hot zone, as the metal or hot air may be bit too warm for comfort. Clean up the adhesive afterward with a citrus solvent, alcohol or vinegar and water.