I know that both Banachek abd Richard Busch have a bending coin routine and David Harkey (in his book Ah-Ha) has one that I love doing. Best to check those sources first. And yes, mentalism is different than magic and signing things tend to make it look more like a magic trick unless of course it is critical to the effect.
Think about how it should look. You openly borrow a coin and make it bend with NOsuperfluous moves or cover....and if you didn't see any way the coin could be switched, then why do you need it marked?
Paul Alberstat http://www.mindguy.com