According to Postman, William Foster was the only one that actually dated his anvils, 1837 in this case. I did not see any clues to what the "TH" means. It is an "Old English" pattern and should have a stamped image of a crown on it. It was probably made in Sheffield, England. I believe the crown image should be just above the name William Foster. As Steve mentioned it figures to be a 100 lb anvil.
May I ask what the condition of the face is? This anvil seems pretty rare in comparison.