No they don't use special serial numbers unless the customer pays for a special number.
Some commemorative models have serials that include letters related to the event being commemorated.
The "CS" 1911's are just part of a normal serial sequence.
Colt Custom Shop guns can be difficult to ID unless you have the original box or a factory letter.
Many Custom Shop guns have Custom Shop fancy grips with CS medallions, but grips are easy to switch.
Without the box or letter, there's often no way to ID a CS gun or a gun that's been worked over post-factory.