Looked at The Glossaries of Words Used in Swaledale, Cleveland, Kent, Surrey, Oxford, Warwickshire, and Whitby English Dialect Society, volume iv, 1873, 1876. I see that F K Robinson is the authority for Whitby. As this book dates after his other Whitby glossary, it may be that Mr Robinson had gathered further information.

[Addendum: The book cited by Kacirk may be a later, augmented edition. The OED1, on more careful inspection, has an entry for poisonful which cites Robinson's Whitby book: "The house was parfitly puzzomful".]

Ceci n'est pas un seing.