What does this traffic sign indicate?

This traffic sign warns you about an upcoming side road intersection where vehicles from the side road have priority or you need to be especially cautious. According to German traffic rules, this warning applies only at the next immediate crossroads or junction.

The key point is that the sign's warning is limited to the next intersection only, not all intersections along the road or until you leave an urban area. This helps drivers prepare to slow down or give way specifically at that next junction.

So, when you see this sign, expect a side road and be alert mainly at the very next intersection. This is why answer 1 ("only at the next crossroads or junction") is correct.