The Cammino Materano has its own credential that grants benefits and must be stamped at each stage to receive the Testimonium at the end of the journey.

The Cammino Materano, like every respectable pilgrimage route, is equipped with its own credential — a kind of “pilgrim’s passport” on which the sigillum is affixed.
The sigillum refers to the stamp that hikers can request at the end of each stage at designated points, certifying their passage. Official sigilla are usually kept by the stage coordinator, while others can be found at affiliated accommodations (bars, restaurants, hostels, churches, farmhouses, etc.).
The credential, a foldable pocket-sized card, must be requested in advance via the website and can be received by mail or picked up in person at the starting location. It doesn’t have a fixed cost, but receiving it requires a donation to support the Association and cover printing and shipping expenses.

Upon completing the trail — after hiking at least 100 km on foot (150 km by bike) — hikers can collect the Testimonium, the certificate confirming completion. The credential not only proves the minimum distance walked but also confirms adherence to the Cammino Materano, entitling holders to hiker benefits like the “pilgrim’s menu” at select restaurants or discounted rates at lodging facilities.
Personally, I’ve never been asked to show my credential to be “recognized” — hikers are usually obvious from afar. So don’t worry: even if you forget it in your pack one evening, you’ll still access discounts at affiliated spots.
The Testimonium can be picked up in Matera if that’s your endpoint, or in Bari if you’ve hiked the Via Peuceta in reverse.

At Martina Franca, you can collect the Xenium, the “midway certificate” for the Via Ellenica — originally considered complete from Brindisi to Matera (though the Brindisi–Alberobello section is now an unofficial variant). The Xenium is available to those hiking the Via Ellenica in reverse from Matera (as I did) or starting the “variant” from Brindisi.

Some pilgrims can’t wait to get home and frame their stamp-filled credential and certificates; others see the stamping ritual as mere formality and aren’t fussed about the parchments. Either way, it’s wise to get the credential before starting the Cammino Materano — both to provide minimal financial support to the project and to contribute to trail statistics: those without one slip through the counts entirely.