Which of the following is NOT allowed under the board's advertising rules?

In the context of the Texas DPS Private Security Bureau's advertising rules, the option that is not allowed is the use of a personal voice in advertisements.

The regulations governing advertising for private security companies are designed to ensure that all advertising is truthful, appropriate, and does not mislead consumers. Allowing the use of a personal voice in advertisements could lead to various issues, such as conveying a personal endorsement that might imply a level of reliability or credibility that may not be universally applicable to all services offered. This could create confusion or misrepresentation in the perception of the services being advertised.

On the other hand, options such as restricting the medium for advertising, prohibiting personal appearances in advertisements, and limiting the duration of an advertisement can be seen as valid regulatory measures intended to maintain control over how private security services present themselves to the public. These restrictions help to ensure that all advertising conforms to a standard that is fair and not misleading, thereby protecting both the companies and consumers within the industry.