Updated with additional information in case of future searches.
From 'The National Museum of the Royal New Zealand Navy' website :
"At the start of World War One the New Zealand Government chartered a number of merchant ships and converted them for troop carrying.
The ships were manned by their civilian officers and ratings, the distinction given to them was a
button-hole badge which declared that they were serving on New Zealand Transports."
https://navymuseum.co.nz/explore/by-...ps/troopships/
.