The decal CRC identifies a decal by its state. Multiple decals which would be
exactly the same would have the same CRC and are culled from the system.
If you store this value with the intention of using it to find the decal again
later, you must update your stored value whenever the decal state changes.
You can detect when a decal changes by watching for the OnUserDataTransformed event.
RhinoCommon (in RhinoCommon.dll)
Public ReadOnly Property CRC As Integer