In the end song 'Best Thing Ever', Will (played by Kevin Quinn) raises his left arm and you can see the tattoo on the underside of his arm.
Will's character is only supposed to be 16, making him too young to be able to get a tatoo.
When Will and Avery are walking through the woods, Will is seen walking with his guitar on his back, but there are multiple cuts of him walking with no guitar. One cut he has his guitar, the next he doesn't.