OOH performance is measurable when you plan for it. Use unique QR codes, short URLs, or dedicated phone lines to attribute responses. For retail, tag offers at POS and compare lift vs. control stores. Analyze footfall with mobile data or in-store counters during the campaign window. Pair OOH with search and social people who see your ad often search your brand; watch for spikes in branded queries. Keep a simple dashboard: impressions (estimated), interactions (QR/URL), store visits, and sales. Over time, you’ll know which locations and creatives deliver the best ROI.