The standard fin markings on 3 Group aircraft equipped with Gee-H was two yellow bars painted horizontally above the fin flash, but not extending across the rudders. The usual method was for two non Gee-H equipped aircraft to formate on one with the equipment, and to release their bombs simultaneously.

5 Group used coloured fins and rudders for daylight ops, mostly red, white or yellow, some solid, others with vertical, horizontal or diagonal bars in black.

1 Group also had them for a while.

(Edited to mention that the Halifax groups also had similar markings, lest HP57 complains!)