Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9930; en-US) AppleWebKit/534.11+ (KHTML, like Gecko) Version/7.1.0.1066 Mobile Safari/534.11+)
IME on attended terminals (i.e. not train station kiosks) if the system prompts for a PIN when you insert the card then there is a button option to get to signature. I've very rarely had a problem with it in such scenarios.
Train station kiosks, on the other hand, are generally a mess.