Handcuffs in a dream speak of a strong bond between people. Perhaps, you are in love, and you experience mutual trust and affection. This interpretation may also relate to business relationships, where both parties trust each other, as well as fellowship.
To see a vein is a multivocal sign, and its interpretation depends on the part of the body where the vein is. To donate blood from the vein indicates that your personal life will change for the better. Lonely people will find someone to love, and couples will probably get married.