Mer, one way to tell real quick is if the two sides are identical. If the border is asymmetric, it's likely cancer. Also if there is a black mole or spot. I have a couple of light brown spots on my face, too, as well as on my arms and the backs of my calves. It's that old Florida sun. These brown spots are not actually "liver spots" but actinic keratoses...which can be a precursor to skin cancer.
Hugs,
Connie