What Could Dark Spots On Stomach Suggest?

I have 3 dark blu/purple marks on my stomach...in various places...I don not remember running into anything of getting poked in the stomach with anything...these are dark and I would think I would know if something had poked me...What could be the cause? I am 60 a little overweight (204) lbs. 5feet 9 in. tall. No medical issues ever..