This is a futile attempt to establish safety, and it is done so that it can be claimed that something has been done.
If some person has the intention to do any harm to others, this person would not be stopped by any restriction to carry any weapon.
The real issues lay much deeper: A growing number of refugees and asylum seekers that want to work, but are prohibited to do so, but at the same time these are competing in an already tight housing market. Raising costs of living, growing inequality, growing envy and a part of the population which is on the brink of shiftig into a nazi movement, with a growing resentment to foreign people. It takes more than putting up a sign that says that weapons are forbidden beyond this point to solve these problems.
Also, in Germany there is no reason ever to walk around with waepons. Compared to other parts of the world it is pretty safe here.
Putting up a sign that states that weapon are forbidden would have the same impact as putting up a sign that forbids wild fires in the forest or flooding near a body of water.