if PFUser.currentUser() != nil {

}

let user = PFUser()
    user.username = "USERNAME"
    user.password = "PASSWORD"
    user.email = "EMAIL"
    // add more fields

    user.signUpInBackgroundWithBlock {
        (succeeded: Bool, error: NSError?) -> Void in

        if succeeded {
            // here the current user should not be nil.
            // if it is then please check for sessionToken
            if PFUser.currentUser() != nil {
                // user is logged in
            }
        }

    }