Maniphest tasks are identified with "monograms", like T123. Other major objects in other systems use other letters (D for Differential revisions, F for files, etc). See Object Monograms for a full list.
Calendar has "E" reserved for it, but the UI doesn't reflect that. Particularly, these things should be supported:
- The main URI for an event should be /E123.
- The crumbs for an event should end in > E123.
- The page title for an event should be E123 Event Name.
- Typing E123 in remarkup should link to the event.
- Typing {E123} should embed a longer reference to the event.
- Typing E123 in global search should jump to the event.
- Mail about the event should identify it with E123.
Note that "E" used to mean "Conpherence Thread". We've mostly moved that to "Z" to let Calendar have "E", but there may be some remnants kicking around.