It is likely that Royal Flying Corps cap badges and insignia were worn by Other Ranks. Officers in the RFC tended to wear either the insignia of the regiment or corps that they had originally joined, or RFC insignia, if they were commissioned directly into the RFC. Canada titles would be worsted embroidery or metal. It is possible that by late 1918, RAF badges were worn, these were very similar in design to the badges worn during the Second World War.
Period images of RAFC Provost Marshal Staff are extremely rare but it appears that the Officers wore standard RFC/Army Service Dress, while NCOs and Other Ranks wore the RFC pattern "Maternity Jacket".
The RFC pattern Maternity Jacket was made of wool serge and as a jacket intended for flying duties, it had concealed buttons. It was worn with either breeches or trousers, and short boots with putties. It appears that collar badges were not worn on this jacket by RAFC other ranks. Army pattern rank insignia was worn on both sleeves by NCOs and on the cuffs by Warrant Officers.
Typical RFC sidecap, in this case, officer's quality with a bronze RFC cap badge and RFC buttons.