Singer & Co. was a Patent Medicine business at 79 Nassau in New York from 1867 until 1869. The Proprietor's name was Julius Singer. "Singer's Hair Restorer" was for sale in the 1872 and 1875 John F. Henry catalogs.
The 1870 Detroit Review of Medicine and Pharmacy examined this preparation and found it to contain 16.39 grains of lead per fluid ounce. That makes them the most "leaded" of all the ones tested. Great! Picture courtesy of Daniel Lakatos.