How can I check if user is signed in with rails devise?

First of all remove do from this line, you don't need that

<% if user_signed_in? %>

Secondly add : after method, it's a key value pair

<%= link_to "Log out", destroy_user_session_path, method: :delete %>

Hope that helps!

You are making a syntax error in method delete. Copy the below code

<% if user_signed_in? %>
    <%= link_to "Log out", destroy_user_session_path, :method=>'delete'%>
<% else %>
    <%= link_to "login", new_user_session_path %>
<% end %>