I’ve given cards like this to many clients, both stuttering and various other reasons as well. It works as well as you use it. People are more kind than you think but disclosure of an impediment is never easy. If you were my client I would give you a card no questions asked, then we would talk about other ways you could disclose that could be more natural for your environment. Clients have been scared police will think they are lying instead of stuttering, so a card is nice proof. But if it’s the person behind the counter at subway, it would be easy to let them know you stutter without a physical exchange