libsigpad implements a userspace driver for Topaz signature pads, at the moment capable of display bitmaps on certain HID USB models. The sample clock shows an example of how to use this library.

libsigpad uses the RawHID library, which it expects to coexist with. It additionally builds with the RawHID makefile (change the source name as needed).

In certain configurations, root permissions may be necessary to use USB devices. If this is the case, it may be mitigated through, e.g. udev rules. See the RawHID documentation for more information.

I found one of these devices at a surplus store missing the pen and documentation but otherwise functional. That being said, there were no free driver available, so I fuzzed the device and later reverse-engineered enough of the protocol to get images. See libsigpad.c for the implementation of the protocol itself.