The English police ...

[duszek]

make a certain gesture when they move a suspect into a police car:

they put a hand on his (or her) head.

Why is that ?

[Arising_uk]

Never seen this? They usually just put an arm up with palm facing forward.

[Hobbes' Choice]

Never seen this? They usually just put an arm up with palm facing forward.

I've seen this time and again. It's to stop a person who is cuffed from banging his or her head on the door frame.

A person not having the use of their hands, can't guide themselves in so easy.

[Arising_uk]

Oh! I'm sorry I misread. Yes it's exactly for the above reason.