Flourescence, Fluorescent Stamp Markings

With a little extra time, I am starting to check out my late 90s, early 00s US stamps with long and short wave ultraviolet light. Some oddities that have me puzzled:
• Scott #3853 has a message that appears with sw light. First line is Mailers, next postmail and the third line was not decipherable by me. What is this?
• I have some stamps with the expected sw luminescence, but also have some markings toward the top of the stamp that appear only with lw light. This is not true of all these numbered stamps, but the ones I found were 3283, 3466, 3476, 3629, 3676, 3629F, 3631, 3642, 3644 and 3751
• Are some of the American Eagle 2003-2004 series tagged and some not.
Thanks for any direction you can provide. I don't really focus on modern stamps, but I am trying to get them placed in the correct place in my album.

John, welcome to the forum. Go to this site: http://stampsmarter.com/features/Tagging_Home.html to find some answers

Peter

Thanks Peter. There is a lot of great information on the site you listed, but I was unable to find any information on the luminous words on Scott 3853 or on why the short list of stamps mentioned would have additional long wave tags.

I'll take a wild stab regarding the 3853 which is one of the 10 design Presorted First Class Golden Eagles with water activated gum. 3853 has a red eagle on a gold background.

Is the stamp mint or used?

If used, it's possible that the wording on the stamp is 'Mailer's Postmark Permit', which would have been applied by the user. I don't know why it's not visible in normal light. Perhaps the ink was somehow bleached out from soaking, exposure to light, or other chemical reaction and it's the residue that's showing up under UV.

See this discussion for examples of mailer's postmarks.

https://goscf.com/t/31250

John, the "additional long wave tags (tagging?)" is probably not tagging at all but the product of "hibrite" paper. Some paper mills add a chemical to their paper to make it look whiter. This type of fluorescence can be seen under Long Wave UV, but is not the same as the taggant that shows up as tagging under SWUV.

Peter

philatomic has it correct

Thanks everyone, especially Philatomoic and Peter4522. The 3853 I mentioned appeared to be unused, but closer examination showed the type referenced to be visible is light red ink. Under sw ultraviolet light the printing really pops. The lw marks are like pairs of extended hashmarks at the top of the stamps in most instances. They don't appear at all under daylight or swuv light. It could be due to the paper, it just looked rather deliberate. Thanks again.