I saw this in the parking lot at the grocery store yesterday. Recognized the octagon shape and the name Watsonian from Jaguar history books. They bought Swallow Sidecar from Tube Investments back in 1956 after William Lyons had sold it off in 1946.
The logo means Watsonian Squire.
Thomas Watson invented a collapsible sidecar in 1912 so he could get it through the garden gate where he lived in Birmingham. The company thrived and is still going strong and importing to the USA, where we put them on the right hand side of the bike.