They are just wooden squares from any craft store ($0.50 each) with metal house numbers I found at Shoppers Outlet for $2 each. These numbers were brass and spray painted Heirloom White. Put them up with finishing nails and use a sharpie to "paint" the nails black.
Disney world does this! Lowes sells the 4 to 6" round PVC pipe with holes already drilled. Purchase an end cap, fill with rock, soil, and plant. I will often put these in the center of a very large pot to stabilize, and add amazing height and color to a container that has trailing plants (no end cap or rock needed if you are placing in a container)