Solved: DAR 51 - Harley Davidson "Cage"

[D-type]

The purpose is obvious.  So all I want is the make of motorcycle.

(If any one knows more, please post it)

[Johno]

1922 Harley Davidson?

[D-type]

Yes it's a Harley Davidson.  I don't know the year.

[Johno]

Not wanting to give up on the Harley Davidson theme. It may actually be a 1918 model Excelsior. Have a look here and see what you think. https://reviewmotors.co/excelsior-motorcycles-usa/    about half way down the page. There is a lot of similarity including the bulge on top of the front mudguard. A similar image including a sidecar can be found by searching. 'motorcycle-police-a-tradition-of-patrol-excellence'   which brings up a page showing a policeman on a very similar motorcycle combination.

[D-type]

It could well be. 
The website I found it on said it was a Harley.  But as they were more focussed on the cage, they might have assumed it was a Harley, not knowing of the existence of other US makes like Excelsior, Indian, etc.  Much as people brand all medium sized vans as "Transits" and all small 4x4s as "Jeeps".
I suggest we leave things as they are unless (until?) someone comes up with a definitive answer.