No, people would not be able to notice that your sunglasses are prescribed, if your SPH power is not that strong. But if your power is strong, the lenses on your sunglassses would be thicker. Just as we cannot identify the non-prescription glasses from prescription glasses.
I can't tell whether the sunglasses have prescription or not. I only know that if the prescription is too high, the lens would be thick. However, if your sunglasss has full frame, the thickness will be less noticeable. Therefore, seldom people will know that your sunglasses are prescribled.