[Zope] Registering just an icon not constructor

[Shalabh Chaturvedi]

In my python product I have a class (IssueFollowup), which I don't want to
register using registerClass because I want instances to be added only
through instances of another class (Issue).

I have the necessary code in class Issue that creates and adds objects of class
IssueFollowup to the folder in context.

1. Is this ok ? (Seems to work but are there any possible pitfalls)

2. IssueFollowup objects appear in the Contents tab but without any icons.
    How can I register an icon without having IssueFollowup pollute the drop
    down list ?

Thanks,
Shalabh