Stone Flesh bug
I can confirm that at least hero panel does not show any difference for Armor when you switch to earth.
May be it is hero panel bug no way to know.
It’s PROBABLY a hero panel bug (fingers crossed). It’s apparently bugged with other things too, such as Plague Form for Necromancer (which, while it may not show on the panel, clearly the extra toughness is still given).
It still gives the 120 toughness. Equip signet of earth and the toughness attribute in hero panel will show the toughness from signet AND from the trait. Unequip and it doesn’t show. Serrated Stones is the same. Tool tip on weapons skills don’t change to reflect the 20% increase to bleeds.