Give this a try:
(defun c:foo (/ s)
;; RJP » 2022-09-09
;; Generate vertical xlines on polyline vertexes
(if (setq s (ssget '((0 . "LWPOLYLINE"))))
(progn (foreach e (vl-remove-if 'listp (mapcar 'cadr (ssnamex s)))
(foreach p (vl-remove-if '(lambda (x) (/= 10 (car x))) (entget e))
(entmakex (list '(0 . "XLINE") '(100 . "AcDbEntity") '(67 . 0)
'(8 . "XLINE") '(100 . "AcDbXline") p
'(11 0.0 1.0 0.0)
)
)
)
)
;; Make layer not plot and color 128,128,128
(entmod (append (entget (tblobjname "LAYER" "XLINE")) '((290 . 0) (420 . 8421504))))
)
)
(princ)
)