Depends on the adhesive.
There are several diferent adhesive bases and depending on which, are more or less readily disolved by different solvents.
My first line of defense is always Varsol/Stoddard solvent/Paint thinner/Mineral Spirits. If that won't get it I delve into my solvent arsenal, usualy in this order. Acetone, lacquer thinner, MEK (methyl ethyl ketone), toluene, xylene, xylol. I get most of this stuff at the big box. I prefer the blue one these days. I have never seen any of these products damage wood or gel coat. If these fail you can try aerosol label/decal remover but just like paint remover, it contains methyl chloride which at best is some seriously nasty crap and can damage gel if not removed in time.
If none of those do it 5 to 10 years or so of sun exposure will embrittle the adhesive and then a finger nail will get it.