Nice catch on the graffito! Once in a while I think there's a
good story to be told about the
graffiti on
ancient coins. I came across an interesting article by Liampia (2008
AJN) when trying to research my own graffitoed Boeotian AR
Stater: "NIKA, ΛEIA:
Graffiti on Sicyonian and Theban Staters in a New
Hoard from
Boeotia / Beginning of 2000"
[LINK]. That particular deposit of coins was basically a post-battle donation, like a tithe from the plunder, dedicated to
Nike.
More often, the
graffiti I see is something like the crosses commonly found on
Byzantine gold coins, which may be there for many different reasons (e.g., blessings intended for the purchase, the
money, or the ruler depicted), including that
medieval European and Levantine Christians would inscribe crosses on pretty much any surfaces they could.
But finding a pattern, or repeated symbol/phrase, like the
Caracalla above, seems unusual and worth paying attention to.
I don't know what could come of it, but I've found something similar with one of my Carthaginian EL Staters (
Jenkins-Lewis Group V, c. 310-290 BCE). It has a pair of Deltas (or triangles or character from another alphabet/syllabary) on the
reverse -- a big one above the
horse, and a small one to the right. Since
buying it, I've seen that same graffito on about a half dozen other examples, usually of very similar dies (i.e., triangle on
reverse, usually above
horse, sometimes two as on mine):
(1)
Carradice &
Price (1995: pl. 24) 300 (BM ex.); (2) Platt 21 April 1914, Lot 15
[Cat. LINK, INHA]; (3) Sontag 12, Lot 48
[LINK]; (4) HJB BBS 70, Lot 10
[Cat. LINK, Archive]; (5)
CNG 90, Lot 372
[LINK]; (6) Ars Classica #16, 3 July 1933, Lot 942 (probably?)
[Cat. LINK, HEIDI].
(7) My example =
Gorny & Mosch 265 (Sammlung H.I. [Süddeutschem Privatbesitz]), Lot 668
[LINK] = Jacquier 44, 138:

For comparison, here is just one of the others (NOT my coin), ex. #3, the Sontag 12 specimen (
Jenkins-Lewis Group VI, c. 310-270 BCE ?)
[LINK]:

I don't know what that means, but the fact that I've found 6 or 7 casually looking makes me think there were a lot more of them, all from coins struck at more-or-less the same time (about 290 BCE), and then later circulated. Perhaps these were given to coins from a certain large one-sum payment. If I find some in any
hoard reports (I haven't looked) or other archaeological context (like the article on Thebes Staters cited above), it might be possible to draw more inferences.
If they were all
applied at the same time, and shortly after being struck, that might also give us information about the sequence and timing of
Jenkins-Lewis Group V & VI EL Staters. (E.g., That those groups were struck at about the same time, rather than after a long interval between issues.) I haven't really read up enough to know what specific implications might be.
Or it might just remain an interesting mystery about which to speculate!