Baldcoin is a currency occasionally found in the main world of YWOT. It began to crop up occasionally in early 2018. It is usually found in various areas around the main area, appearing as the phrase "BUY BALDCOIN".
We can only assume that Baldcoin is some sort of cryptocurrency based on Bitcoin.
It's likely that it is based upon a meme from streamer Jerma985, who in one of his streams, blurted out "Buy Baldcoin" when he meant to say Bitcoin.