PHP isset() $_POST не работает

Постоянно выводит false

<form class="signup-and-login-form signup-form" action="/signup.php" method="POST">
                        <?php if(!empty($errors)){
                                echo array_shift($errors);
                            }
                            if(isset($_POST['do-signup'])){
                                echo 'true';
                            }else{
                                echo 'false';
                            }
                            ?>
                    <input type="text" class="input-form has-sucsess" placeholder="Введите логин" name="login" id="login">
                    <input type="password" name="password" placeholder="Введите пароль"  class="input-form" id="password">
                    <input type="password" name="confirm_password" placeholder="Введите пароль"  class="input-form" id="confirm_password">
                    <label for="do-signup" name="signup" class="do-signup-label">SIGN UP</label>
                    <input type="submit"  name="do-signup" value="displey-none" id="do-signup">
                </form>