Back in the olden times (the 90s) I remember using vinyl decals only as letters in my windows. Sometimes when I needed to save money I would have to cut out all the letters myself (trust me it was hard, the material is so unforgiving). Nowadays you can get just about anything pre-made and pre-cut!
I highly advise using decals as an effective way to add visual interest and dimension to your display, especially if you’re artistically challenged (meaning you can’t draw for beans!). They are relatively inexpensive, if you take care of them, because they are reusable.
Here’s one source I found whose selection I like - The Surface Store
(images via: The Surface Store)