Actually, sometimes it's not about the words, but about the context. I agree regarding the tattoo's, however, John has nothing to compare with what he was seeing, so the closest word he could use was 'charagma' which doesn't only mean tattoo, but is defined as follows:
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HELPS Word-studies
5480 xáragma – properly,
an engraving (etching); (figuratively) a mark providing
undeniable identification, like a symbol giving
irrefutable connection between parties.
5480 /xáragma ("brand-mark") was originally any
impress on a coin or a seal,
used by an engraver on a die (stamp, branding iron).
5480 (
xáragma) later became "
the identification-marker" (like with an
owner's unique "brand-mark").
[Ancient documents were validated by such stamps or seals (see Plutarch,
Agesilaus, 15:6;
De Lysandro 16:2,
ala DNTT, 2, 574).]
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Therefore, it is not good exegesis to just hone in on the word tattoo and ignore the other descriptive words. In your post you said "I have based none of my beliefs on what John had to compare what he saw" but you should. Because it is needful to take into consideration that John in describing the mark, he is seeing something that he has nothing to compare to except for the word 'charagma' and we most definitely have to take that into consideration.
Another good example of this is found at the sounding of the 2nd trumpet. John says, "I saw something like a huge mountain all ablaze that was thrown into the sea." Well, during John's time they did not have scientific classifications for planets, stars, meteorites and comets. Therefore, everything besides the sun and the moon were stars to them. In John's vision he sees this huge mountain, he is most likely seeing an asteroid coming through the earths atmosphere which is why he describes it as being all ablaze. However, he cannot say I saw an asteroid coming through the earths atmosphere and land in the ocean. Therefore, it was a huge mountain to him on fire.
Also, a tattoo will not allow you to access your bank account to credit and debit it, that is unless it is some type of schematic tattoo, which it could be. Regarding the mark, we already have a literal RFID chip being inserted under the skin which is being used to make purchases (buying), so we have a match there and it is not tattoo. However, whatever the mark ends up evolving into, it will go on the hand or the forehead and will be used for virtual buying and selling, which is crediting and debiting.