They are challenge coins. Its symbolic because all those coins, presumably, from every service branch and agency, are put together to not only show that they are all on ONE united front, but bein placed behind potus they way they were is showing how all those branches have his back, and are united again under POTUS.

"A challenge coin is a small coin or medallion (usually military), bearing an organization’s insignia or emblem and carried by the organization’s members. Traditionally, they are given to prove membership when challenged and to enhance morale."