A water-worn, broken slab with a possible 'Tau' cross incised upon it has been found at Rhendoo and is now kept at the Manx Museum.  The stone has not since been included in the Manx Cross series.  A six-figure grid reference was provided which places the discovery close to several others which are not of similar date if this is a Christian memorial or monument.  No early medieval ecclesiastical or religious site is known in the vicinity.