What must you reckon with when you see this traffic sign?

You correctly identified that this sign means you must expect several hazards related to road work. According to German traffic rules, this warning sign indicates that there are workers present on or near the roadway (men at work). Additionally, you should anticipate construction materials on the roadway that could pose obstacles or dangers. Furthermore, there might be construction vehicles entering or exiting the site, so you need to be cautious about unexpected traffic from these vehicles.

This sign warns drivers to slow down and be vigilant because the normal road conditions are disturbed by construction activity, which can include people, equipment, and materials. Understanding this helps ensure safety for both drivers and workers.