undefined method `user_signed_in?' for #<ProjectsController:0x007faead1853e0>

Are you using devise for authentication? i haven't used it myself but by looking at the devise code and documentation it looks like you should do before_filter :authenticate_user! in the controller (or some parent controller class) where you want to use helpers like user_signed_in?.

Note that since Rails 5.1 you have to use before_action instead.