It is "Department of Corrections". It is common in some prisons.
I am watching an American movie named Primal Fear.
An attorney was meeting his client who was accused of murder. There is the printing of D.O.C on the back of the T-shirt the defendant wore.
Does D.O.C mean Department of Correction?
Do suspects wear that mostly in the US if you know?
In the UK, there's no similar clothing. However, click HERE to read an interesting answer from someone who has been in prison in the UK. I don't normally set much store by Yahoo Answers but this guy does seem to know what he's talking about.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.