I feel that signature skills somewhat limit the capability of players to feel skilled in areas that don't strictly relate to their class.
A possible way to fix this is to have all skills capable of being raised to legendary, with the existing signature skills being trained for a class, and classes getting a bonus number of trained skills equal to their int modifier. This would still give class a head start in the stuff they are good at while still alllowing for more unusually skilled people, e.g. The Diplomatic Barbarian or The Athletic Wizard.
This would also increase the value of intelligence, and open skills up to more players. I think this might be a good idea, does anyone have any feedback on this concept.