I'm sticking my ski boots in my checked luggage next month and will put my skid-lid in my hand luggage. I did consider wearing it whilst boarding if I couldn't fit it in the ruksack, as it's just a form of hat - right? ;o)
Some airports don't allow ski helmets in hand luggage, Grenoble for one, where they had a sign up last winter, advising that both ski boots and helmets would be destroyed if presented in hand luggage at security.
There seems to be no common policy (or common sense) within Europe on this.
The only way of ensuring that the integrity of a safety helmet has not been damaged in transit is to keep it with you.