From Wikipedia:
Pink Quote, informally known as the Pink Sheets, is an electronic quotation system operated by Pink OTC Markets that displays quotes from broker-dealers for many over-the-counter securities. Market makers and other brokers can use Pink Quote to publish their bid and ask quotation prices. Starting in 1913, and prior to the creation of the electronic system in 2000, these quotes were printed on pink colored paper by the National Quotation Bureau. The term Pink Sheets is also used to refer to a market tier within the current Pink Quote system.
The Pink Sheets is not a stock exchange. To be quoted in the Pink Sheets, companies do not need to fulfill any requirements (e.g. filing financial statements with the SEC). With the exception of foreign issuers, mostly represented by ADRs, the companies quoted in the Pink Sheets tend to be closely held, extremely small, or thinly traded. Most do not meet the minimum U.S. listing requirements for trading on a stock exchange such as the New York Stock Exchange. Many of these companies do not file periodic reports or audited financial statements with the SEC, making it very difficult for investors to find reliable, unbiased information about those companies.
For these reasons the SEC views companies listed on Pink Sheets as "among the most risky investments" and advises potential investors to heavily research the companies in which they plan to invest.
Buying Pink Sheets shares is supposed to be difficult. Broker-dealers are enjoined to weed-out unsophisticated investors who may get an e-mail or word-of-mouth tip about a small stock. Many Pink Sheets stocks may only be registered for sale in one state so that the only way to purchase the stock is to make a DRIP/business/unsolicited/accredited or other sophisticated form of investment. Many registered representatives do not even know how or if they can sell them.
From Stramark Capital Group:
粉单市场(Pink Sheets)由私人设立的美国全国行情局于1911年成立，为未上市公司证券提供交易报价服务，从上市要求、规模、交易情况看，粉单市场与OTCBB比较类似。该市场隶属于一家独立的私人机构(Pinksheets LLC)，有自己独立的自动报价系统—OTCQX。
粉单市场是一种集中报价服务系统，收集并公布造市商在柜台交易中的实际交易及价格信息。在粉单市场交易的公司不需要向SEC或任何其他管理机构做公告。粉 单市场的交易不会列出股票的卖价和买入价。需要一名做市商及40名左右的股东。一般是通过其股票的做市商来买卖粉单市场的股票，企业在美国其它大交易所 NYSE，AMEX，NASDAQ或OTCBB被摘牌后，仍然可以在粉纸市场挂牌进行股票交易。申请在粉单市场挂牌的程序和申请OTCBB挂牌一样，但在 粉单市场上财务报告不需要经过审计。
粉单市场报价的证券
在粉单市场报价的证券包括：一、由于已经不再满足上市标准而从NASDAQ股票市场或者从交易所退市的证券；二、为避免成为“报告公司”而从OTCBB退 到粉红单市场的证券；三、其它的至少有一家做市商愿意为其报价的证券。
粉单市场的任务其实就是通过使用艺术级的国际互联网科技对柜台交易市场（OTC）创造更大的透明度，以便于给投资者提供做投资决策时所需要的必要信息。粉单市场没有股票交易或管制的实体。价格是由柜台交易的造市商提供的。
粉单市场的结构特点
A. 采用做市商交易制度。只有经SEC注册作为NASDAQ会员的做市商才能为粉红单市场上的股票报价造市。报价系统与股票发行人之间无直接联系，证券发行人 不用在粉红单市场申请上市和报价，而是通过做市商进行报价。做市商不了解或不经发行人同意也可以在粉红单市场上报价。
B. 报价没有特别的上市标准要求，只要做市商填写一份真实反映发行人当前最新状况的211表格提交市场审核即可，并不要求审查发行人的财务状况等。粉红单市场 是美国唯一一家对上市既没有财务要求，也不需要发行人进行定期和不定期的信息披露的证券交易机构。
C. 粉单市场仅仅是一个报价服务系统，不提供自动交易撮合，也不执行自动交易指令。它不是一个发行人上市挂牌交易系统，没有上市标准。不受SEC注册要求的管 制，不必向SEC上交财务信息和其它的公司常规文件，没有信息披露的要求。证券发行者在粉红单市场被报价无需支付费用。
粉单股票类型
- 参与型(sponsored)，由公司挂牌交易
- 非参与型(unsponsored)，由经纪人挂牌交易
两种粉单股票均透过纽约银行这类美国存讬凭证的存讬银行发行－－纽约银行资料显示，679支粉红单股票是参与型，220支粉红单股票是非参与型。
外国粉单股票，不管是不是参与型，在股票代码最后一位用字母“Y”标记。投资者也应该注意，如果发现一支粉红单股票的代码中不止一个字母“Y”，如大众汽 车，那就应该谘询经纪人到底是什么意思，因为那可能表示不同的股票等级。
