Free Signs too Free?

It does get aggervating with non op/admin players asking 24/7 when im on for a free sign. I usually let them have it if its like tools or wood or stone, ocassionally i will put a diamond sign but i say if we start to see the towering diamond buildings that are nothing but diamond we replace it with wood and get rid of the sign. Maby put that at the spawn that abusing the free signs we give them will resuslt in the signs being taken away. any other ideas?