De acordo com o site:
Souvenirs are virtual pieces of art that you can discover and display on your profile page. They are associated with a particular location and may also be bound by time.
There are two ways to discover a souvenir. The first is to log a geocache within the souvenir zone. For instance, if there were a souvenir for Hollywood, CA and you logged a geocache in Hollywood, you would be awarded the souvenir. The second is to search for a geocache using the Geocaching Application for iPhone or Android when you are within the souvenir zone. Text on your profile page will indicate whether the souvenir was discovered by logging or through an application.
If there is a time parameter to the souvenir, as there will be with those discovered at Mega-Events, the souvenir zone will expire at the end of the period. You can still obtain the souvenir by logging your attendance online.
If you have previously logged a cache in a souvenir zone, the souvenir will be added to your profile at a later date.
We hope that you enjoy discovering these unique pieces of art!
Sinceramente, ainda não percebi bem o que é, mas à primeira vista acho que não vai trazer nada de novo ou realmente importante.