I recently bought a used saddle, in great condition, for $85. It was Martin & Martin, made by the London Harness Agency. I really wanted to know more about them, as I've never heard of them before. It took a long time, but I finally got some information. So I'm posting this to help anyone who has one of these and is having trouble with finding information.
"MARTIN & MARTIN, London Harness Agency. No. 285 Fifth Avenue, No. 1713 Chestnut Street, Philadelphia.—The importation of /^l harness has long been an important feature of the commerce of the metropolis, and has enlisted the attention and energies of / 1 some of our ablest business men. The largest, and by far the most prominent house engaged in this line is that of Messrs. Martin & Martin, whose London Harness Agency is situated at No. 235 Fifth Avenue, and who also have a branch at No. 1713 Chestnut Street, Philadelphia. The parent house was originally established in London in 1821, and the London house and manufactory are now situated at No. 103 Gloucester Road, South Kensington. Owing to the excellence of their productions the firm were long since appointed saddlers to Her Majesty, Queen Victoria, and they have repeatedly won medals over all competitors at exhibitions held in London and Paris. The house in this city was established in 1872 by Mr. E. M. Earle, and in 1887 Messrs. J. M. And G. Martin succeeded to the control. 'The Messrs. Martin are natives of London, Eng., and have resided in the United States the past ten years. They have an expert knowledge of all the details of the harness business and know how to most satisfactorily meet the demand. The store occupied has dimensions of 25 x 125 feet, is handsomely fitted up, and contains the largest and finest stock of choice goods in harness and horse-furnishings to be found in the United States. These goods are all made in London and are the best in the world. The trade supplied is with the elite only, and our leading citizens are patrons of this model establishment. The firm fill orders received from any part of the United States, all goods being guaranteed to be exactly as represented. The Messrs, Martin are zealous in meeting all the wants of their numerous customers, prompt in filling orders, and will be found most courteous and reliable merchants with whom to have dealings." Source: History and commerce of New York, 1891 - Google Books
And then I found various adds, the most interesting being in a copy of the Rider and Driver, The Rider and driver - Google Books, pg. 32.