Usually the paper part of the sticker washes away in the washer and you're left with the residue or adhesive that is used on the back. Quite often, the adhesive has attracted dirt or lint and the stain looks almost black. Begin by heating undiluted white vinegar in the microwave until it is quite warm. Use a sponge and saturate the sticker area with the warm vinegar. Allow the area to "soak" in the vinegar until the adhesive loosens.
Rinse the area with cool water. Treat the area with a prewash stain remover and launder as usual. Check the area after laundering. If any residue remains, repeat the treatment. Do not put the garment in the dryer until all adhesive is gone. If the garment has already been through the dryer, it make take several attempts to remove all of the residue.
You can also use acetone (nail polish remover) on the residue. Test first to be sure the shirt is color stable. Put the sticky side of the shirt face down on a white towel. Pour the acetone onto the back of the shirt and rub. It may take several attempts to get all the residue to come off.
If the garment is dry clean only, point out and identify the stain to your professional cleaner. If you are using a home dry cleaning kit, be sure to treat the stain with the provided stain remover before putting the garment in the dryer bag.
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