Hello DanielD and welcome to the forum,
Your image is too poor for us to know exactly what you have. However, I believe that it is a #632 and is not one of the very valuable rotary wast issues. If you can take a picture from directly above, then you can use a photoshop like program to compare the horizontal to the vertical perforations. I suspect that they won't match. You can do the same thing physically with another stamp. Pick one that matches either the horizontal or vertical perforations, then rotate it 90 degrees (1 quarter turn) and then compare it to the other set of perforations.
https://goscf.com/t/45086 has an example image that shows how the vertical and horizontal perforations don't match and other information.