Here a quick Tutorila on How to make Security Fences for Warhammer 40k Terrain. All you need for the Fence some wood or cardboard for the base. Then you will need Mesh Wire.
You can just glue Printed out Signs on Plastic Card and attach them to the Wire once painted.
I made these 2 Warning of Tyranids Signs.
You can also add some 1/35 scale Barrels & Containers.