QR codes
QR codes are the simplest modern way to attribute response. A unique code per drop area or per round points to a landing page, where every scan is timestamped. Most smartphone cameras now scan QR codes natively, removing the friction that existed a few years ago.
Dedicated phone numbers
A separate phone number printed only on the leaflet attributes every inbound call to the campaign. Call-tracking providers can capture origin postcode where the caller permits caller ID, which lets you map response to drop area.
Unique landing pages
A short URL — for example yoursite.com/leaflet-n12 — printed on the leaflet sends traffic to a dedicated page. The page can pre-fill an offer code, log the visit and attribute downstream conversions cleanly.
Offer codes
A printed code redeemable in store, online or at point of order is the oldest and still one of the most reliable methods. Different codes per drop area lets you compare postcode performance directly.
Response attribution
The strongest setups combine two or three of the above. A QR code for digital response, a dedicated number for phone response, and an offer code for in-person redemption together cover almost every customer path.
Campaign analytics
Tracking the response side answers "did anyone respond". Tracking the delivery side answers "were the leaflets posted". For full confidence in a campaign you need both. See GPS tracked distribution for delivery verification, and campaign results for example outcomes by industry.