It may be possible if no information or anything shows that someone is the owner. But we should not do it because the credit is not ours. We also don't know if anyone knows about it but they keep quiet because it doesn't belong to them. You can try asking the casino staff if you find it so that you won't experience problems gambling. If you use the credit, you may be accused of being a thief, especially if the credit owner returns to the slot machine and wants to take the credit back. That will be a problem for you. And the casino will know if you have used those credits.