I would have put your cell phone number on the "NO TRESSPASSING" sign you put on the tree the stand is in.

If the person wishes to have their stand back, they can have it back after calling you( and after YOU call the DNR). Remember, You are not stealing the stand, you are only temporarily holding the stand that was mis-placed on your property.

Negociate a meeting place and time, and have the DNR there waiting with you.