This fascinating structure is a lightship, which was used from 1927 - 1975 in the River Humber estuary. It's now open as a museum, which must account for the octopus tentacles!!!
Alternative: They could be showing support for the Seattle Hockey team: Seattle Kraken : The kraken is a legendary sea monster of gigantic size and cephalopod-like appearance in Scandinavian folklore.
Well, the tentacles are a fun addition to the lightship! Although the lightship is supposed to be open for visitors, I haven't yet managed to visit when it has been open. I'm sure you will find Kingston upon Hull a fascinating city, with much to see. It is a far more interesting place to explore than it's reputation would suggest, and it has an excellent set of museums in the 'Old Town'. Hull Minster is a gem to explore as well. I hope you enjoy your time there and I look forward to seeing your photos of the city. Fav!
https://www.nhl.com/kraken
(couldn't resist)
Ian