You may add a message to be displayed on the sign and specify the fontsize, color, and bgcolor. Look at the sign you wish to display text on. In game chat, type  /silt <message> [<fontsize: number>] [<color: hex value>] [<bgcolor: hex value>]. This is available on our Scourge and Survival servers. You can view the command on the server by typing /silt in chat.

Example: /silt "Welcome to the Community Centre" 20 #ff0000 #000000