A new version of GPU-Z just hit the web. GPU-Z 1.11.0 follows the latest news about NVIDIA GTX 970 class action lawsuit where NVIDIA will payback $30 to each owner of a GTX 970. One way to prove that you have a GTX 970 is to show a screenshot of GPU-Z that now displays the full device ID. GPU-Z 1.11.0 also brings support for BIOS saving on GTX 1060.
Another tool to display the full device ID is GPU Caps Viewer. Here a screeny of the GTX 970 with its device ID: