• ?Service promptly. Dark/Defunct Tier There are two types of companies that will fall into this memorably named tier:
•No Information: You will see this category listed with a stop sign as a symbol. These are companies that are defunct or have not filed any information with either the SEC or the OTC Disclosure and News Service within the last six months. These companies are the ones that you need to be very cautious about. •Gray Market: The symbol for the gray market is an exclamation point. Companies in this category do not have a market maker. These companies are listed on neither the OTCBB nor the pink sheets. This category has no market transparency. Trades in this category are made by a broker-dealer and reported to their self-regulatory organization (SRO). The SRO will distribute the trade information, which is how prices can be tracked
I Just went to the Investopedia website and found this.