I've never seen that icon before. Are you using Creo 3?
There are many ways to create and control parting lines using basic Creo Parametric. Essentially, parting line = draft hinge. In the standard Draft and the Variable Pull Direction Draft tools you can make the draft hinge be surfaces, edges, datum planes, and sketched curves. Hinging off of a sketched curve is a really powerful capability. Combine that with the Variable Pull Direction Draft and you can get some pretty wild drafted surfaces/parting lines.
