"If you find the "strange relic" treasure in the game, you will quickly recognize it to be a precursor orb from the Jak games. There are strange symbols wrapped around the orb. These symbols correspond to letters of the alphabet as already known from the Jak games. So I used this to decipher it

The top row of the egg says "naughty dog".

The bottom row with bigger symbols says "manmad".

At first I thought, what the hell is a manmad? So i googled it.

It seems that Manmad is the name ..."

"Speaking in a recent Three Speech interview (Part 1, Part 2), Naughty Dog co-president Evan Wells said Uncharted was developed as the first part of a franchise, and we are likely to see sequels in the future:

"We developed Uncharted as a franchise. The pulp action/adventure genre lends itself perfectly to serialisation and continued episodes, which is one of the reasons we were attracted to it.

[Regarding the team’s next project] …but even if we don't do an Uncharted sequel right away..."