Colour on the logo is off. What else would you look for?
On those two jerseys specifically, from what I can tell just from those pictures?
SENS:
- color is off
- the front logo is "bubbling" at the nose, which means it's made of twill, which means it's fake
- the interior neck tagging is off
- customization on the back is off (albeit very slightly, but in a way that's easy to spot if you're looking for it because of the consistency in this problem among fake jerseys)
- you should be able to see the large stitching outline for the fight strap on the back. You can't because they used a cheap small-ass strap with no twill reinforcement.
BRUINS:
- everything I said about the Sens jersey
- shoulder patches are "folded", which is like a huge giveaway. Honestly, that's the biggest giveaway: that perfectly folded shoulder patch to me makes it 99.99999999% fake.
- bubbling all over the customization on the back.
There's probably tons more clues in person, but those aren't the best pictures.