Virginia law requires all contractors to include their license number on all documents to include contracts, proposals, bid forms, and advertising. It would always be prudent to ask to see a copy of the license before signing any contract. Once you have the number, you can confirm the license by calling the State Board for Contractors in Richmond at (804) 367-8511. Additionally, you can check their information at the Department of Professional and Occupational Regulation website atDPOR License Lookup.
Here is some additional information from DPOR and links that will be helpful when searching for a licensed contractor.