app/views/signatures/index.csv.erb
<%- headers = ["First Name", "Last Name", "Email", "Zipcode"] -%>
<%= CSV.generate_line headers -%>
<%- @signers.each do |user| -%>
<%- row = [user.given_name, user.family_name, user.email, user.postal_code] -%>
<%= CSV.generate_line row -%>
<%- end -%>