The Chief's Medallion
In the XIXth century, the various administrations in Washington gave the chiefs in Indian delegations a much prized medallion with an engraving of the sitting president on its metal disk.
The painting at the left shows a Hotcâk chief named Nâka ("Tree") wearing two such medallions. [1]
For other examples of Chief's medallions see Tcizanhaka, Amisquam, Huwanika.
Sometimes the medallion may have other inscriptions or images engraved upon it, as shown below in the painting of Wakan, a member of the Snake Clan. [2]

The illustration at the left is from a painting of a Hotcâk war chief of the Elk Clan named Huwanîka ("Little Elk"). [3]
The silver disk appears to contain a portrait of Martin Van Buren, President of the United States (1837-1841). The medal looks very much like silver coinage and could be easily assimilated to the older idea of a "money necklace." The more ancient necklaces were presumably of wampum shells which functioned in many ways like silver coins.
For the symbolic role of the money necklace and chief's medallion, see the Deer Clan Origin Myth.
Notes:
[1] Thomas L. McKenney and James Hall, The Indian Tribes of North America (Edinburgh: John Grant, 1934) 1:146.
[2] McKenney and Hall, 2:308.
[3] McKenney and Hall, 2:306.