I've flown several times recently and had no trouble with kilt pins like the X-Marks with the short studs. I do leave the claymore pins at home.

I travel with a nylon guide pouch that I use for a sporran when I need to carry lots of stuff. It has an several inner pockets, and I attach my pins to the inside of the pouch just behind the over flap. That way they pass through the x-ray attached to something and are easily inspected by the TSA agent.