At 27 weeks pregnancy I had a blood test for rhesus c. They found cold antibodies. They say this can do no harm to my baby, but what does it mean for me?

Basically nothing. It may perhaps be a bit trickier finding the best donor blood should you need a transfusion, but there's enough c-negative blood available. Consider autologous donation should you be planning surgery -- always a good idea in any case. Congratulations on your upcoming delivery, and best wishes.