AR 670-1 Para 1-16. And it says next to nothing.
1–16. Wear of identification tags and security badges
a. Identification (ID) tags. The wear of ID tags is governed by AR 600–8–14.
(1) Soldiers will wear ID tags at all times when in a field environment, while traveling in aircraft, and when outside
the continental United States.
(2) Personnel will wear ID tags around the neck, except when safety considerations apply (such as during physical
b. Security identification badges. In restricted areas, commanders may prescribe the wear of security identification
badges, in accordance with AR 600–8–14 and other applicable regulations. Personnel will not wear security identification
badges outside the area for which they are required. Personnel will not hang other items from the security
badge(s). The manner of wear will be determined by the organization that requires wear of the badges.
Don't bother looking up AR 600–8–14 because it says even less.
So what ever your Sergeant says is gospel. Rule number one. The Sergeant is always right.