This is an exceptionally rare envelope of "black matboard" or silhouette witches that Dennison issued about 100 years ago! During their first few years of issuing packaged goods (1912-1914), Dennison's inventory numbering system is easy to understand. Once their sales of such pre-packaged merchandise took off, their numbering system became so complicated and convoluted that today there seems to be no way to understand their methodology. In the earliest years, Dennison assigned numbers only. Soon, they added an H before the numbers, sometime with a hyphen, sometimes without. (It seems so very random.)
Mark B. Ledenbach's vintage Halloween collectibles blog.