A perch (navigation beacon) is marked with the annotation 'Red' at the southern end of a causeway (see NPRN 518934). Other contemporary depictions suggest a red buoy with a perch.

Sources include:
Historic Admiralty Chart 1170-A4, RCAHMW Digital Collections sourced from UK Hydrographic Office (published 1839)
Historic Admiralty Chart 1174-A6, RCAHMW Digital Collections sourced from UK Hydrographic Office (published 1839)

Maritime Officer, RCAHMW, October 2011.