In an Activity Diagram, I can create a guard for an object flow (Papyrus 0.9.0/Juno).
However, unlike a guard for a control flow, the guard for an object flow is not shown in the diagram (not visible). Is there any way I can make the guard visible for object flows, or is this by design?
it is just a matter of Workspace preferences to get those guards available for each new objectFlow.
For existing ones, you can adapt visibility with "manage connector labels" once you selected the object flow.
Sure this is not really consistent with other properties managed through "appearance" tab of property view. You can submit a bug (enhancement) for that.
Hope it helps