There are good posts on this forum about PSR. A good way to distinguish how to use it, is...
The Signpost describes the outside view, e.g. a physical activity
The "in terms of" part describes the inside view from the character(s) perspective, e.g. how does it feel/look from within doing something in terms of e.g Investigation
(Outside Doing) A detective runs through a suburb and interviews people in the street... (Inside view Investigation, from the detectives perspective) He needs to figure out how the crime could happen