Detailed Instructions: Given a travel related situation, and given a specific question about the situation, summarize the question into a title
Problem:I have been invited to a conference in USA. I am going to apply for a B1 visa. Unfortunately the invitation letter doesn't have a signature on it. Only the email id and the website is there. Would the letter be valid in this case?

Solution:
Is a signature mandatory for a B1 visa invitation letter?