Don’t use their name. It’s against the contract and even without the contract, it’s bad form without chatting with the client first (consider just the NDA...). Not to mention they’re big, your small, you can’t afford the legal trouble.

Instead you might say in a sales call the type of companies you’re working for. When I worked as a consultant we might not say “Careerbuilder” was a client, instead we’d say “one of the top 5 job search companies in the US”.

And future protip: don’t undervalue yourself in contract negotiations. If you truly offer something unique and valuable, don’t give it up without serious due consideration.