I am sorry I missed your initial inquiry.
I am not aware of any laws or regulations that create requirements for a loan participation agreement. The document is a contract between two business entities. Generally contracts are signed by all parties to the contract, and the signatures are original signatures. Since your institution is a party to the contract you may insist on original signatures. Your institution can refuse to complete the contract if the selling institution refuses to provide original signatures. Simply do not sign your copy or do not provide the purchase price.