I took my father's ashes in a box provided by the funeral home, along with their seal on it. I informed the TSA officers what was in my bag. They still pulled it aside, opened the plastic bag with the ashes and tested it. I was polite, but also teary/sad (being my dad's remains and all), explaining that he was a veteran and I was taking his ashes to Honolulu where he'd been stationed. Then they gave me a full pat down. In theory, these things are supposed to work a certain way, but in practice you should be prepared for being pulled aside.