What is the difference between the following traffic signs?

Traffic sign 135 alerts about a pedestrian crossing ahead, while traffic sign 306 marks the place of the crossing.

There is no difference between them.

Traffic sign 306 alerts about a pedestrian crossing ahead, while traffic sign 135 marks the place of the crossing.

Traffic sign 135 is placed in non-urban roads, while traffic sign 306 is placed in freeways.