On the Pokemon status screen, underneath the Pokemon and to the left of the custom markings, is a small blue pentagon:
This doesn't seem to be present on Pokemon obtained through the Pokemon Transporter from Gen V:
I've looked into it myself, and popular opinion seems to be that it's either some kind of "Legitimate Pokemon" mark or simply to indicate that the Pokemon originates from Gen VI.
The latter seems far more likely to me, but do we know for sure what this blue hexagon means?
Best Answer
It's apparently a Kalos Region checker. Pokemon native to Kalos have it. It is not, as some say, a hack checker. This is easy to confirm since Pokemon Transporter straight-up won't import many hacked and some not hacked pokemon.