If you need to have a sign outside, advertising something, using an acrylic sign holder is the best way to go to avoid weathering. A metal holder will rust over time and anything wood will fall apart if it rains too much. Acrylic can be in any color and will always look good. A simple cloth can wipe it free of any dust or dirt. If you have one with a clear cover for the sign, your sing can be made of paper or cardboard and still be protected from the elements.
If you are displaying things for people to look at the same things apply. Acrylic displays are good to use. You can place things in them and they will not get dirty. Customers can easily see what is for sale. If the items are things that are easily stolen, you can have the case lockable so you have to get the items for the customer. It might be a bit of a hassle at times, but it will save on your inventory loss. These can be small enough to sit right on your counter or big enough to be on the floor and hold many or big items.
Another way to display merchandise you have for sale is with a slatwall. Attach it to one of your walls and hang your merchandise up on the slats. You can hang a wide variety of items regardless of their size. You arrange the holders so they are not all mixed in together. They can be as close together or as far apart as you need them to be.