I like unusual badges and signs, for example the Lamb and Flag, sometimes referred to as Agnus Dei, lamb of God. The picture here is of the Arm and Hammer sign on the side of Goldbeaters’ Hall in Manette Street, next to Foyles in Charing Cross Road. The building itself was the fictitious address of Dr Manette in Dickens’s Tale of Two Cities, resulting in the street being so-named. Goldbeaters produce gold leaf in the traditional manner, that is to say smashing ribbons of gold alloy (typically there is a little copper in the mix) with a cast iron hammer until it is a few thousandths of an inch thick. Hence the sign.
But the arm and hammer – not an especially common sign – is also an emblem of the Worshipful Company of Farriers, for obvious reasons. In recent centuries it has become a popular device of manufacturing trades unions and labour movements. There’s an interesting essay on the subject by Kim Munson, here. Lastly, you may be familiar with Arm and Hammer toothpaste, along with other domestic potions. A rather bizarre brand, I think, but there you go.