Which sign indicates a bike crossing?

Answer: A — diamond sign with a bike symbol

The sign that indicates a bike crossing is a diamond-shaped sign featuring a bike symbol. Diamond-shaped signs are typically used for warning indications and are often associated with situations that require caution, such as approaching a designated area for bicycles to cross. This design effectively alerts drivers to anticipate cyclists in the area, ensuring that they reduce speed and remain vigilant. In contrast, while other shapes like rectangular, circular, and triangular may form part of the traffic system, they are not standard for bike crossing alerts. A rectangular sign might provide information or regulations but won't specifically denote a crossing. A circular sign usually conveys regulatory or prohibitory information, and a triangular sign generally indicates yield or caution but not specifically for bikers. Therefore, the diamond shape with the bicycle symbol is the recognized and correct choice for signaling a bike crossing.