Its not a hint and its pretty clear he did show barrier haki.
This is marco taking kizarus attack
As we can see the attack is blocked rips marco to bits and he heals himself
This is shanks vs akainu
As you can clearly see not only is the punch blocked all the excess magma is clearly held back by the barrier
now marco vs akainu
Weve seen marco block with his fruit and regen this is completely different not only is marco not being hit by the magma and regenerating, just like shanks the magma is being held back. Ergo Barrier haki.