Chatzitza by tefillin - when covering a cross etched on the arm - v1 #26 by R' Aaron Cohen

Rav Oshry describes the overwhelming burden of the Jews conscripted into forced labor, leaving well before the break of dawn and returning at night. These Jews faced the question of when they could put on Tefillin. One courageous individual secretively put on his Tefillin at daybreak while marching to work, but he was caught by the Nazi guards. After cruelly beating him, they engraved a cross onto his arm where the Tefillin Shel Yad is placed. This individual was painfully embarrassed at this symbol being seen by others as he prepared to put on his Tefillin. Could he keep his arm covered to conceal the cross, or would this invalidate the fulfillment of the Mitzva by causing a separation between the Tefillin and his arm?

Reference Material (pdf)