Those interested in more about the Tientsin Volunteer Corps (TVC) should look at the article 'The Tientsin Volunteer Corps in the Boxer Rising, 1900' which appears in pp. 179-181 of volume 36 of the Journal of the Society for Army Historical Research. It can be accessed, through JStor, at the link below (registration required),
https://www.jstor.org/stable/44228890
The article contains the following photo of Privates F A Kennedy, A S Annand and F R Scott. The object on their head is described as a 'black lambskin cap, similar to that worn at the time by Canadian troops in Winter kit'. They were armed with the Martini-Henry.
There is reason to think that Arnold Bassett Watts was the brother of James Hector Watts, also of the TVC and the hero of the Siege of Tientsin in 1900 (a James Arnold Watts - their father? - died in Tientsin, aged 59, between 1901-1905.
James Watts rode through enemy territory to the Naval station at Taku and was successful in seeking a force to relieve Tientsin when the defenders were on their last legs. For his pains, he was awarded the Rettungsmedaille am Bande, a Chevalier of the Order of Leopold and was made a Companion of the Order of St Michael and St George.
The TVC, as a man, refused to receive their China Medal as, being civilians, they were initially refused the 'Relief of Peking' bar awarded to the regular soldiers who took part in the defence of Tientsin. However, subsequent questions in Parliament ensured that they were properly so recognised.
https://api.parliament.uk/historic-hansard/commons/1903/apr/02/medals-for-tientsin-volunteers
Finally, James Arnold Watts, the putative father to Arnold Bassett Watts, was described as a pilot in the entry of his death. If his son followed in his father's footsteps, I wonder if CPS might stand for something line China Pilot Service?