You will be fine with them - I travelled in 2009 with a bag full of buttons on a trip to a few cities in the US and Canada where I gave them out to other fans of the band who I was going to see, and it was no problem.
However, I would put them in a separate plastic bag and just lay them in the bucket next to your bag - otherwise they show up as a mass of metal on the x-ray. They took them out on my first stop and the security lady gave me the tip to do that afterward and had no problems presenting them separately in a ziplock bag.
They are definitely not a prohibited item.