Whatever design you choose to use? make sure it's legal theirs laws on making coin that can be used as a currency make sure you read up on The laws about  these things? and also seek Professional Legal Advice about doing something like this. http://www.communitycurrencieslaw.org/currency-laws/

U.S. Code › Title 18 › Part I › Chapter 25 › § 489
18 U.S. Code § 489 - Making or possessing likeness of coins

Current through Pub. L. 113-121. (See Public Laws for the current Congress.)

Whoever, within the United States, makes or brings therein from any foreign country, or possesses with intent to sell, give away, or in any other manner uses the same, except under authority of the Secretary of the Treasury or other proper officer of the United States, any token, disk, or device in the likeness or similitude as to design, color, or the inscription thereon of any of the coins of the United States or of any foreign country issued as money, either under the authority of the United States or under the authority of any foreign government shall be fined under this title.