Like anything else, you need to learn what you can and can not do with it. I use it a lot here in florida where it gets really hot. Light colors work best as they reflect heat. Darker colors absorb and then expand. Even with expansion, if you allow for it and give the material room to move, you're okay. If the entire sign is made with the same pvc, it will all expand together. Where you have to be careful is when mixing with different materials that have different expansion rates.
Thicker material is more stable, however you can laminate thinner parts together with pvc cement and build added strength into it. Lots of tricks to learn, but it can be a great product to work with once you learn some things about it.