The sign reads:

contents of time capsule

1. a mobile phone you can call and leave messages on

2. something that will last for a shorter period than the capsule will remain closed

3. the things that used to be above where it's buried

4. the earth from the hole it's buried in

5. the sign saying where it is buried

6. fossils

Visitors could call the mobile phone in the time capsule, hear its muffled ring and leave an anonymous answerphone message to be buried with the capsule.