police officer = any normal rank or SI (station inspector)...
equivalent to army enlistee/specialist/sergeant/warrant
officer.
SPO = senior police officer (Regulars are degree holders only or
NSF/NSmen with min dip/A) ... means go through 9 months training
and commissioned with sword as Inspectors....
non uniformed....no such thing la... everyone got uniformed.
plainclothes is just for IO (investigation officer/CID) etc who
need to be not recognised as police so easily. But they still have
rank/uniform, but normally don't wear. They are also either normal
police officers or Senior police officer...normal ranks like the
rest.