Tracking subscriptions in BLOX from a specific event

I am opening an event for Street Fairs/Community Event tables were we talk about the paper and offer a deal for customers to subscribe. I need to track this separately from other subscriptions. Is the promo code field the best bet? Can I set up the promo code without a discount? Has anyone done this successfully in the recent pass? We are also just setting up access IQ +. Thanks, Thea Giardina, www.newjerseyhills.com

ps: we have 13 papers that cover 4 counties so tracking is important