If your job is to monitor this forum and assist users, why couldn't you manage to suggest that the other users use the stamps feature, since it was clear that what they were wanting was only the signature image? These folks are spending hundreds and thousands of dollars on your products and they deserve better than this.
In fact, Apple is more than capable of processing signatures using their Keychain utility, it's just that they have elected not to include that functionality into Preview. As far as how the signature is created, and how it should be processed, that's all covered by public facing documentation.
When it comes to the actual cryptographic operations we license the software from RSA.
The PDF specification is public and the Acrobat SDK even has an example of how to create your own signature plug-in. If they can get by with using a custom stamp then that's fine by me, but that wasn't the thread topic. When Mobius Strip asked about flattening the signature into a bitmap image that I suggested using a custom signature appearance, because the progenitor of the thread was asking about digital signatures. It was dsaks who originally asking about creating a digital signature and that's what the core of this thread is about.