We have two other patterns in our TCC Database of Patterns and Sources which feature similar reverse marks. I'll attach an image. ABG appears to be Allerton, Brough, & Green, 1831-1859, of Langton, Staffordshire. Not a guarantee, but a good probability of a match with your pattern. BTW, we don't have this pattern in our Database; would it be okay to use your images for a new entry?