No one can remember when the practice started, but in the slowly warming days of Spring, the men came out and secured the cards to banisters, gates, or whatever bit of architecture lent itself to speed and ease. 
Wishes of wellness, cleanliness, political harmony: what was written upon them did not quite matter as much as the thought that was behind them. 
Left alone, they would spin out their intent on the wind, and only the most curmudgeonly would immediately take them down, cursing the uselessness and waste. 
The Japanese have something similar in Tanabata, but here, no one ever thought to call it anything, and so it has no name.