You say you have a schedule with many projects. Is that a dynamic master with subprojects or simply a single large project with many summary lines representing individual "projects"? In either case those "external" dependencies will appear as normal predecessors and successors although in a Master/Subproject structure the external links will contain the full path to the external task such as shown in this sample.
If you want to isolate all the external links, a simple custom filter such as this will do it:
Applying that filter will produce:
If however you have just a single large file with multiple "project" summary lines, you can set a Flag field for all dependencies that cross summary groups and then filter on the Flag field.
Does that give you what you want?
John
Go to, View > Task Views group > Other views > New. You will get a pop-up asking if you want to create a single or combination view. Select "single" and you will get the View Definition window. Note that a view is made up of several elements, including a view table and filter. So, create the filter for the Flag field and create a view table to specify which fields you want to show along with the view formatting. Then give your custom view a name and you're all set.
On your other question, you can elect to display any Project field in or around Gantt Bars. Go to, Gantt Chart Format > Bar Styles group > Format >Bar Styles. In the Bar Styles window lower half select the "Text" tab and where you want the field name to appear. Note however that adding text to Gantt Bars can make the display very busy and often harder to see so go easy on the custom text.
If you really want to get fancy, a macro could automatically identify which tasks are in which summary group, select those that have dependencies that cross between summary groups, set the flag and apply the filter, all with the click of a Quick Access Toolbar icon. Pow! Bam! You're there. 🙂
John