We need to have some common milestones among projects which are logically separated in different groups, and we are not finding any way to share something if projects are not in the same family or tree.
We propose that global administrators (and only them) may be able to create milestones which cross boundaries. It could be done using a special flag in the milestone,flag which would limit critical details (like original source item) and management to administrators, while project leaders and member may see and refer to these milestones in their projects without having the possibility of modifying them and without knowing the source item.
So, for example, an administrator could. alternatively:

• create directly in the project B a "special" milestone pointing to a sub-project/task/milestone in project A
• create a milestone related to whatever project/task in whatever project and then create a "special" referring milestone where it is needed

In this way only administrators could manage cross-projects milestones, but this could be a great help to us.

If there is an alternative way to do this, please enlight us.