What kind of numbering convention are you currently using at your shop? I was just curious because I have been asked to come up with one and I have devised something simple:

For Requirements:
RQ1000 (Parent 1)
- RQ1001 (Child)
- RQ1002 (Child)
RQ2000 (Parent 2)
- RQ2001 (Child)
- RQ2002 (Child) ... and so on ...

For Test Cases:
TC01001 .. and so on ... (for Parent 1 and its lower hierarchy)
TC02001 .. and so on ... (for Parent 2 and its lower hierarchy)

How do you guys do it?