They are safe to wash in your washer as long as it has no agitator. I did mine after researching a lot. I found this.
https://www.blueovalindustries.com/xt0255.html
I did mine, let it air dry. Came out perfect. I would spray some fantastic on heavy soiled areas before putting it in the washer...
Here in Ontario we have to have a front plate as well. May of us run without on our pleasure or weekend cars. Its a stupid law that make zero sense. We pay for a new plate sticker every year for the rear only. No point on having one on the front IMO.