Bicycles: No Parking Sign

This is a sign telling people not to park their bicycles here. It is located in front of the library. What is more interesting is the yellow plastic water tank on it. There is a white cap on top where the water can be added or drained. Do you know why it's there? The additional weight of the water keeps the sign from blowing in the wind. In the past, I have seen signs blow down the street.