Strange text at Roydon Lock

On Friday we moved on from Burnt Mill Lock on the Stort to below Carthagena Lock on the Lee. Again, we were fortunate with the weather with the rain holding off until we'd tied up. Roydon Lock is welcoming ...

… and there is a piece of text on the sign which took me a little while to work out.

It reads: "Ore stabit fortis arare placeto restat".

Geddit?

Dobb's Weir Lock is another marked with red and green discs on the bottom gates.

But why?