A SignatureCycle is the list of all the people that have to sign off on a change before the change can be approved.
The time it takes for a change to go through a SignatureCycle depends on:
ExtremeProgramming environments try to have very short SignatureCycles -- typically the customer, two programmers, and whoever writes up the user documentation (if any).
In a good SignatureCycle, each reviewer takes responsibility for those aspects of the change that are related to the reviewer's area(s) of expertise.
A long SignatureCycle is an AntiPattern.