What does it mean if i have a simian crease on both hands?

Can mean nothing.: This is usually associated with syndromes like fetal alcohol syndrome, and the trisomies like down's syndrome, etc.. But it does not have to be associated with them or anything. To have it on both hands is rare: %5 population. It is apparently more common among asians and native americans than among other populations.

Simian crease: a single crease in the palm vs the multiple transverse creates many have may mean nothing at all . While rare about 1 in 30 of so called "normal" people have this. There is also a long list of syndromes and illnesses associated with a simian crease. But if you had one of those you'd know it , be born with it and you can't catch those things from others

May be nothing: If you have only this particular sign and no other signs and well otherwise, it means- nothing. If it comes with the constellation of some other specific signs and symptoms, pediatricians look for certain chromosomal disease, such as down's syndrome.