Well, it's in the same shape as Nailsea but I don't think it is.
It says in Miller's "Glass of the '50's & '60's" that this trapped air bubble technic was used throughout the 20th century. Nailsea Glasshouse in Bristol operated 1788-1873 so we can rule that out.
Scimowser's hat probably doesn't have an un-ground pontil mark anyway.