If an embargo is used for a Bitstream, but the Item is publicly readable, there is no information about the embargo. The only difference between a Bitstream with restricted access and one with public access is the request a copy button, which will be displayed for users without access only. The Open/View button is shown as well, without any information that it may forward to the login form. Users with access to the Bitstream see absolutly no difference. The same code that is used to list Bitstreams on the Item page, is used to generate the preview for reviewers. As reviewers have access to restricted Bitstreams, they do not see the request a copy button. So reviewers currently cannot see if there is a access restriction on Bitstreams in the Task preview. To see if a Bitstream is restricted or not, a review has to edit the policies of the item of take a look on the metadata review page, which is accesible only in the edit metadata workflow step.
A solution would be to label restricted Bitstreams. While doing so it would be good slightly change the View/Open button. If a Bitstream has an access restriction the button name should make clear that the button may forward to the login form.