You could always display some religious apparel while in uniform.
I don't recall you could wear crosses etc. that were visible, unless you were a member of the chaplain service, I told more than one of my squad/platoon members to pull in their crosses peace signs etc. behind their t shirt and if it didn't stay to take it off. In 13 years I cannot recall one marine/soldier ever wearing a pin-cross/star of david etc etc .....
one of the purposes of a uniform is a form of structural/egalitarian cohesiveness, there is no I in team, no individuals so to speak or individualism aside from your name tag and awards. Your beliefs are your concern and the military has in fact taken steps to make a point of that especially when it regards religious/sexual mores etc. as of late... I really don't see the purpose of this.
Then you aren't recalling correctly.
10 U.S. CODE § 774 - RELIGIOUS APPAREL: WEARING WHILE IN UNIFORM
(a) General Rule. Except as provided under subsection (b), a member of the armed forces may wear an item of religious apparel while wearing the uniform of the members armed force.
(b) Exceptions. The Secretary concerned may prohibit the wearing of an item of religious apparel
(1) in circumstances with respect to which the Secretary determines that the wearing of the item would interfere with the performance of the members military duties; or
(2) if the Secretary determines, under regulations under subsection (c), that the item of apparel is not neat and conservative.
(c) Regulations. The Secretary concerned shall prescribe regulations concerning the wearing of religious apparel by members of the armed forces under the Secretarys jurisdiction while the members are wearing the uniform. Such regulations shall be consistent with subsections (a) and (b).
(d) Religious Apparel Defined. In this section, the term religious apparel means apparel the wearing of which is part of the observance of the religious faith practiced by the member.