You are welcome to do whatever makes you comfortable before starting the WOD. The "official" CrossFit Warm-up is in the April 2003 CrossFit Journal.
2-3 rounds of 10-15 reps of
Samson Stretch (do the Samson Stretch once each round for 15-30 seconds)
Overhead Squat with broomstick or PVC pipe
Back-extension or supermans
Note that for a workout that's dip or pull-up-centric, you might want to do something else in the warm-up.
For further information about ISP CrossFit, email Health Management Specialist Troy Torrence at firstname.lastname@example.org.