LC Designer has been replaced by FormsCentral in Acrobat XI. Currently FormsCentral does not support signature. Sorry for that. But you can post a feature request and vote it if you like.
Hi Shiyao Bao, thanks for the reply. I need to create some PDF forms that can be used on the iPhone to capture a customers signature. As the signature support is not a feature of FormsCentral, it looks like I will have to uninstall XI and re-install Acrobat 9 Pro. I'll post a feature request and vote it (I'm not sure why Adobe have removed a feature availble in previous versions of Acrobat? Doesnt make sense?) Thanks anyway.