Writing on the Tefillin straps: Is it permitted to write the name of the Tefillin’s owner on the inner side of the straps? Is there a difference between Tefillin of the arm or of the head in this matter? Are all kinds of ink kosher for this purpose?
Answer: It is permitted to write a name on the underside of the Tefillin straps, both the Tefillin for the head and the Tefillin for the hand, and one can use any writing material, but not red ink