The watermark on UX4 is similarly located to the watermark on UX3. Often only a portion of the watermark is visible. I see many hopeful UX4 submissions to APEX which are UX5. If you feel you really have a UX4 please submit it to one of the expertising committees for confirmation.
Thanks but I still don't know where to look! I acquired 1000's of stamps, covers and postals from a gentleman that was more a hoarder than a collector. As for the UX4's, there are about 30 of them mixed in with 100's of postal cards from the 1880's to the 1900's. I just want to correctly identify them when selling so as not to waste a true collector's precious time. Thank you!