A driver's license is not valid:

A driver's license is not valid due to several conditions, all of which contribute to the legality and usability of the document.

First, the license must be signed by the licensee; a lack of signature could indicate that the driver has not accepted the terms of the license or that the identification is not confirmed as legitimate by the bearer.

Second, the expiration date is a crucial determinant of the license's validity. Once the expiration date has passed, the license is no longer legally acceptable for operating a vehicle, regardless of any other factors.

Lastly, if the licensee is prohibited from driving under the Criminal Code of Canada, such as in cases of driving suspensions or bans due to criminal convictions, the license cannot be utilized to operate a vehicle legally. This ensures that individuals who pose a risk to public safety are not permitted to drive.

Since each of these scenarios independently invalidates a driver's license, they collectively support the notion that a driver's license can be rendered invalid under multiple circumstances. Thus, the best answer encompasses all these factors.