What does this sign (+) indicate?

The sign represented by a plus symbol (+) indicates that another road crosses the one you are traveling on. This sign is commonly used to alert drivers that there may be traffic from a intersecting road, which is crucial for ensuring safety at intersections. It serves as a warning to reduce speed and be prepared for potential cross traffic, allowing drivers to assess their surroundings and proceed with caution.

In contrast, the other options provide different meanings that do not align with the visual symbol of a plus sign. For instance, a side road ahead on the right would typically employ a different symbol indicating a right turn or a side road sign specifically, while a merging lane would typically be represented by a sign alerting to a lane drop or merger due to the change in road configuration. Similarly, a yield ahead would be marked with a triangular sign instructing drivers to yield to oncoming traffic, which clearly distinguishes it from the crossroad sign represented by the plus symbol.