This sign indicates the point at which...
A)the recommendation to travel at a speed above 40 km/h ends.
B)the obligation to travel at more than 40 km/h begins.
C)the obligation to travel at least 40 km/h ends.Correct
The sign indicates the point from which a previous 'Minimum speed' sign, in this case 40 km/h, ceases to apply.
Do not confuse with the advised maximum speed sign, which recommends an approximate travelling speed, in km/h, that is advised not to be exceeded, even when the meteorological and environmental conditions of the road and traffic are favourable.