This sign is a distance marker, indicating the distance to a level crossing. The distance is marked in three stages, with the number of diagonal lines on the sign indicating how far you are from the crossing. If the sign shows three lines, it means you are at the beginning of the distance to the crossing. (Two lines would indicate 2/3 of the distance is left, and so forth.)

The picture in the question shows the first marker (with three line), which is placed together with the warning sign indicating an upcoming level crossing.

When the speed limit is 60 km/h or lower, the warning sign should be posted 50-150 metres ahead of the hazard.

When the speed limit is 70 km/h or higher, the warning sign should be posted 150-250 metres ahead of the hazard.