נ נח נחמ נחמן נחמן מאומן

The ערוך השלחן writes (Y.D. 288:11) 

"You should stop those who write שמות הקדושים

or שמות מלאכים and call it a שמירה by placing

it on top of the doors & windows.

This is a חוצפא כלפי שמיא (Chutzpa towards the

heaven)

Hashem commanded us to place only Mezuzos

on our doorposts and they add other things

for שמירה which is the way of Amei Ha'aretz, 

women* and those who are missing דעת. It is a 

Mitzvah** to be מוחה." 

* Before the establishment of Bais Yakovs 

** With this email I am Mekayam the Mitzvah 

of לשמוע לדברי חכמים and I am מוחה