This is my theory for what it is worth - given what we know.
We cannot at the moment find any RN service record for him and that may be because he may have served in the Mercantile Marine Reserve (MMR). Little in the way of records survive for these men. Many were merchant seamen who signed T124 agreements and variants and who kept their civilian pay and conditions but were subject to naval discipline - they were Naval Auxiliary Personnel (NAP) and wore RN uniform. They were under the command and control of the RN.
He was a signalman (crossed flags) according to his branch badge on his right arm.
There was an Arthur E. Smith - signal boy aboard the Admiralty Yacht WINTONIA who served in the (MMR). See the attached medal file.
WINTONIA (ex-LADYE MAISRY), hired yacht, Pendant No 020. Built 1894, 168grt/233TM. In service 3.11.14-6.4.15. May have served as wireless-equipped A/P Group Leader or in special yacht squadrons, at home or in Mediterranean.
This yacht would also be similar to HMY BACCHANTE.
do you know if there are crew lists anywhere?
As those ships were effectively under Royal Navy control and not operating under Mercantile agreements there won't be any crew lists unfortunately.
Regards
Hugh