You can probably tell by the smell. Acrylic hardly has any odor. Enamel is pretty stiff. If it's laquer it will take the top of your head off
Dip an old piece of sprue in it and then dunk it in some water. If the paint immediately dissolves it's probably acrylic. Do the same thing and let it dry, then spray it with some Windex. If the Windex dissolves it, it's acrylic.