Connect one PVC Elbow to each of the two 6' long PVC legs. You can use PVC cement if you have it, but frequently just pushing the PVC together will suffice.
Connect each end of the 50" long PVC crossbar into the two PVC elbows. Use PVC cement if you have it.
Lay the large 'U" you just created on the ground.
Place the 48"x12 coroplast sign on the ground centered between the legs with the three grommets at the top of the sign laying on top of the crossbar.
Carefully mark the crossbar with a pen or sharpie where the centers of the grommets are.
Use a 3/16"drill bit to drill straight through the crossbar where you marked the grommet holes. These holes are for the zip ties to secure the sign to the crossbar.
Find the spot where you want to display your sign.
Drive one piece of the 3' rebar 12 to 18" STRAIGHT down into the ground. Be sure there are no pipes, electrical lines, etc. where you are going to install the rebar.
Place one of the legs over the rebar. Position the other end of the sign where you want it. Mark the ground where the second leg is. Move the sign out of the way.
Drive the other piece of rebar 12 to 18" STRAIGHT down into the ground.
Lift the sign holder up and slide both legs down over the two pieces of rebar.
Use zip ties to secure the top three grommets to the crossbar. DO NOT secure the bottom of the sign to the legs.
Installation Tips
If you are installing the sign holder on a slope, you can make the downhill leg longer to keep the crossbar parallel.
If you have regular wind where the sign is, you can use add a couple of heavy washers to the two bottom corner grommets using a short bolt and nut. This extra weight will help keep the sign hanging straight down in light winds and move less in heavier winds. Be sure to use galvanized or stainless steel bolts and washers to avoid rust getting on the sign.
Modifications for Use on a Bench
You can use the same principles outlined above, but make shorter legs and secure to the bench in one of two ways:
Make a PVC Foot:
Make a 'T' foot (one T piece of PVC with two 6-8" feet sticking connected to the T to give the sign stability.)
If needed secure the foot to the bench using zip ties if your bench has grates. If not, you can screw galvanized pipe straps over the top of the PVC feet into your bench.
Rebar and Block
Cutting a 4"x4" treated post into two blocks 4" long. Use a drill bit that is a tiny bit smaller than your rebar diameter and drill a hole in the center of one side of the block. Go down 2 inches. Do the same for the other block. Pound a 12" piece of rebar down 2" into both blocks. The shorter PVC legs will slide over the rebar. Secure the block to your bench with a galvanized L bracket.