Which sign warns you to slow down because you are approaching a double curve?

The correct answer is the Curves Ahead Sign, which is specifically designed to alert drivers that there are curves in the road coming up. This sign is critical for safety, as it informs drivers to reduce their speed in anticipation of navigating these curves, helping to prevent loss of control or accidents. This sign is typically placed far enough in advance of the curves, allowing sufficient time for drivers to adjust their speed safely.

The other signs mentioned convey different meanings. For instance, the Double Curve Sign indicates there are two curves in succession but does not specifically highlight the need to slow down as the Curves Ahead Sign does. The Winding Road Sign indicates a series of curves ahead, but it often suggests a longer stretch of winding road, rather than immediate curves. Lastly, the Curves Left and Right Sign indicates specific directions for curves but may not universally imply the caution needed for double curves. This makes the Curves Ahead Sign the most appropriate warning for slowing down as one approaches double curves.