My Blue Light Ballot UPDATE!!!!
(media.greatawakening.win)
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The UV lights could be narrow spectrum, tuned to a specific, tight frequency range to look for a watermark of ink tuned to the same frequency. Or the UV light could be used to detect creases as it is done in stamp collecting:
https://www.safepub.com/stamp-collecting-supplies/stamp-accessories-tools/ultraviolet-uv-lamps
https://michaelkay.co.uk/ultra-violet-lamps/which-ultra-violet-wavelength-do-i-need.htm