A sound example of a centralized cryptographic electronic cash was surprisingly published by NSA where they mentioned about "Electronic cash" and "Public-Key Cryptographic Tools" to make Untraceable electronic payments and all of these to be accomplished with the help of digital signatures. For refernce have a look at - HOW TO MAKE A MINT: THE CRYPTOGRAPHY OF ANONYMOUS ELECTRONIC CASH - Laurie Law, Susan Sabett, Jerry Solinas, National Security Agency Office of Information Security Research and Technology, 18 June 1996- Link here
Also the book "The Sovereign Individual" published in 1997 by James Dale Davidson and Lord William Rees-Mogg had mentions of a decentralized form of Cybercash which would be based on public-key cryptography and the author also compares it investment in gold and how it would overcome issues with using gold as a form of money. Here's is a post by the reddit user highlightning the sections from the book and here's the book on Amazon if you'd like to purchase and read it.
Fascinating, indeed. I wonder whether any of these and prior mentioned references influenced Satoshi, or whether he (she?) was just playing around with the cryptographic challenges of a trustless payment system.