Which of the following quotes is considered NOT firm?

The selection of an unpriced indication of interest in the Pink Sheets as not being a firm quote is based on the nature of what constitutes a firm quote in the securities market. A firm quote represents a binding offer to buy or sell a security at a specified price. However, an unpriced indication of interest does not imply a commitment to transact at a defined price; rather, it often reflects a potential interest in buying or selling a security without establishing a firm price level at which a transaction would occur. This differentiates it from the other options, where clearer pricing is indicated, thus establishing a more concrete commitment.

In contrast, an OTCBB issue quoted at 10 bid reflects a specific bid price and demonstrates readiness to buy at that level. A quote given over the phone of "3 to 3.25" implies a firm range of prices where trades can occur, thereby providing actionable pricing information. Similarly, a two-sided quote on Nasdaq indicates a firm bid and ask, displaying clear commitment by market participants at defined prices. All these options embody characteristics of firm quotations, which allows for transactions to happen within specified parameters.