That does look like a nutcracker. Researching a little bit, Samuel Stockton White (1822-1879) was a dentist and made dental tools. Records also do show that he was more of an inventor than dentist and worked with persons like Thomas Edison, Elisha Gray, Alexander Graham Bell and others. It is possible that this is a design he came up with somewhere along the way possibly trying to improve on a design of the time. It is also possible that this may have been his personal nutcracker and he stamped his hallmark on it for personal identification. How did you come across this tool? Are there any other markings on it that could help identify?