3 Pieces of Cowan Pottery

Three pieces of Ohio pottery from Cowan Potters Inc . 1913-1931 . The first photo shows a piece of their mass produced line , 8 1 /4 " tall Larkspar Vase with a Ink stamp (COWAN) on base . The other pics are two ash trays in different glazes with same Gazelle relief , they have impressed stamps and also letters impressed on base ; tan one has the letter J and red/ brown(a chip on 1 edge ) has the letter E . Would anyone know what the impressed letters represent ? Thanks for looking (-;