The following is the e-mail response from Potbelly Sandwich Works when asked which of their menu items are vegan:
Thank you for reaching out to Potbelly with your questions! Our Nutrition Calculator will show you which of our items are vegan (http://www.potbelly.com/Food/Nutrition.aspx), and you can also make our Mediterranean sandwich vegan if you order it on the Regular Bread and without the cheese. Our Regular bread does contain L-cysteine, but it is made from non-animal sources. Our sandwiches are typically all prepared on the same surfaces, but we would be more than happy to prepare a sandwich on a separate surface, with freshly-changed gloves and a new knife, if you can just let the team at our shop know that you have a strict dietary restriction when you place your order.
I hope this helps–please let me know if you have any further questions!