I'm 33 years old and noticed a very dark flat vein on top of my left hand that starts from the wrist down to my third nuckle ?

All Is Not In Vein: So-I assume it's long and thin and maybe a little curvy?I want you to hang your hand all the way down and see if it fills up. And if it does,then raise it above the level of your heart and see if it goes flat.If so it's a vein.Welcome to the human race.If not, if it stays flat all the time it may be an old occluded vein(? past trauma?).If none of that works, and it's not a tattoo, get it looked at