Create a dummy objective called
Test
Set your score for objective Test to 1
Perform this command:
/setblock ~ ~ ~ standing_sign 0 replace {Text1:"{\"score\":{\"objective\":\"Test\",\"name\":\"@p\"}}"}
Set your score to 2
Do NBT Copy on the sign (middle mouse wheel and ctrl) and place it down
You will notice that the sign has still the old value (1) instead of the new (2) even if this sign was new placed
I am not sure if this is intended but I guess not
Can confirm. The NBT data of the sign after using /setblock becomes:
Thus using pick-block will grab a sign that has that data. This is probably working as intended for all I know, perhaps as a way to translate what to display.