Is there a lock rating system in the US?
The simple awnser to your question is no. 

However their are a few other nations that have well established bike lock reviewer's, including "Thatcham and Sold Secure in the United Kingdom, ART in the Netherlands, SSF in Sweden, and VDS in Germany" (1) 

With this in mind I'd suggest considering that individual bike lock brands will likely have their own security rating, which you should take into consideration depending on how much you value your bike.