Brown patches on one of your hand would be ecchymoses.
There no other symptoms.
It is due to leak of blood from capillaries in the skin.
The disease is called purpura
There are many causes.
In you case, it may be local trauma.
You do not worry.Consult dermatologist
Have perfect diagnosis ,and there after proper treatment...ok
I hope you got my answer.
Dr. Ilyas Patel MD