If your BOM has conformal coating material with fluorescence dye, you can mark your board using the coating material without introduce any new material from approved BOM.  It will be visible under UV, but not visible.  However, if you introduce a new material = some ink, you may need approval (unless it is your design). 
 
My 2 cents.
                                              jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask]
Sent: Wednesday, June 18, 2003 1:15 PM
To: [log in to unmask]
Subject: [TN] "Invisible Ink"

Group, I've been asked a strange question. Anyone using any type of "secret" markings or "invisible" inks to make sure they get the original boards back after rework? Sounds like a bit of paranoia to me. Reminds me of the quip, "Last night someone robbed my house and replaced everything with an exact duplicate!". ---------------------------------------------------
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