Thanks for the detailed reply! I see your reasoning for thinking it’s a SUP — the signage is not very explicit at all.

The cycle infrastructure here was upgraded a couple of years ago, somewhat temporarily, as a diversion while the riverside path was closed. See https://www.lancaster.gov.uk/news/2020/jun/changes-made-to-cycle-route-diversion. Before then, there was less cycle infrastructure on Caton Road, and the crossing opposite SHC Hire was much simpler (if I remember correctly).

Following the diversion route on 
https://storymaps.arcgis.com/stories/28e119001b074dfd80266367e8543a5c shows how it was put in on the east side of Caton Road, and was always designed to cross opposite SHC Hire.

So I don’t think the segment of pavement just south of it was ever designed to be a shared use path.

The crossing at the south end of it only has a picture of a person above its buttons, not a person and a bike. The pavement on the other side of the crossing (around Bridge Square Apartments) is definitely pedestrians only.

So to me the balance of evidence is suggesting that this change should be reverted, but I appreciate it’s not clear on the ground! Thanks very much for the time you’ve put into this (and other edits round Lancaster!). :)