I can be many colors.
Or just red, maybe brown.
Colour code, Code red and Code brown
I'll tell you where things went wrong,
Unless I'm out on the town.
Error code and Post code
I can be assembled, broken
Or even on fire!
You can break a code, (Thanks Rubio!) an assembly code and (Thanks @Sconibulus) Fire Code
You could find me in a d-ring
Or policing new hires.
A (Thanks @Deusovi) decoding ring and (Thanks @Rubio) code of conduct
At the bar, you can read me.
And monkeys know me well indeed!
A bar-code and (Thanks @Sconibulus) Code Monkey
And, of course, the title: 'A secret riddle'
Talking in code