OP cloth arm badge

[mooke07]

Hi all,

Another pic of my father as a lance corporal in Lincolnshire regiment (on left) with a soldier with swagger stick under his arm wearing an OP arm badge (possibly Leicestershire regiment cap badge). What does this stand for? I thought the P for police as Dad did policing duties with a signals unit. Anyway best I ask the experts. Is that Dad's rank stripe on his rolled up sleeve?

Cheers and thanks in advance, Dean.