An account administrator is the person who registers and has the right to add users to the account or remove users from the account. There can only be one account administrator.
You can view the different user accounts and their roles by logging in at MyVCG.com, then click on Account at the top, then the Contacts link. Here you'll see a list of users and their permissions.
If you are in the sign and graphics industry and your company is on Signsearch, your company is already registered and the main contact for your company will serve as the account administrator.