This early sign was used by the Philadelphia Contributionship for the Insurance of Houses from Loss by Fire - the first property insurance company in the United States. The company, founded by Benjamin Franklin, would provide these signs to those who held a policy with the company. The policy number would be indicated on the mark.
The Philadelphia Contributionship is still around today providing insurance. They provided these particular cast iron marks in the early 20th century. The mark measures 7"W x 10"H.
AB - 104517 - 050422