Leo Burnett Risom chairs  

Hi,I recently found four chairs. Two are Risom C120 armchairs, standard height. The other two may be Risom, but I can't find anything that looks like them. They all have excellent vinyl upholstery that matches. Here is the question...The two actual Risom chairs are marked with metal tags that say "Leo Burnett Co. Do not remove." plus a number. I am wondering if the Burnett name adds value, since he is so famous in advertising. I guess Mad Men was based on his office. Thoughts? What are the two worth?