I know the original poster is relatively new to the hobby, so it's worth mentioning that when someone says it is "unknown," that conclusion reflects a consensus of the hobby after research, and not just the point of view of a single person who posted.

Some collectors have been able to gather the production records of chip manufacturers, and post those to the internet. If we can't find a record of a particular design, we call them unknown, unidentified, or "UFCs" (unidentified flying chips).

We also often tend to call chips "illegals" when they are not associated with a legal casino, but that term often encompasses private sets made for people (or clubs) that may have featured card games with personalized chips but didn't necessarily operate illegal casinos.