The sign you're referring to is the Detour Announcement sign. This sign indicates that there is a detour in place due to road works, obstacles, or other situations that prevent the normal flow of traffic. When you see this sign, it means you should prepare to take an alternative route.

The detour is typically in effect for a specified distance or until further notice, and it's important to follow any detour signage that follows this initial sign to safely navigate around the obstruction. Be aware of the changed traffic conditions and remain vigilant for instructions and guidance as you follow the detour route.

Always adhere to speed limits and be cautious of potentially confused or slow-moving traffic as drivers adjust to the detour.