Okay, so it's a nice but not outstanding coin, not particularly rare or valuable. But why in the world would anyone write a catalog number over the reverse with indelible marker? Couldn't they just put it in a holder? Would sure make me think twice about donating any of my coins to that museum.
Quite interesting, I appreciate the MET article describing the usage of the coins in southeast Asia. I had no idea they actually circulated so far from home, but it sheds some light on the source of the little "collection" of ancient coins found during excavations of a castle in Okinawa recently.
It has long been standard museum practice to write an acquisition or catalogue number in India ink on objects, so long as the marks could be removed fairly easily. So they are often found on metal, glazed ceramic or glass but not much on paper or cloth. Micro laser-engraving is being used in some cases, but many professionals feel that this is an unacceptable changing of the object (“First, do no harm” applies here as well), even if the mark is not visible with the naked eye. Notice how, if an object is reconstructed in any way, the new parts will always be readily distinct—just look at Classical pottery, where crack-filler will be in a totally different color than any part of the original pot. And coin holders are very new, after all, so maybe we will start seeing them more in the future.
Not surprising. There was extensive trade between the West and East during the Roman times. That, or as @Roman Collector points out, it could have been lost by a collector. I'm missing a few coins myself actually - I wonder what archaeologists will think when they excavate my sofa. No doubt BuzzFeed will run a headline: YOU WON'T BELIEVE WHERE THIS ROMAN COIN WAS FOUND!!
Writing reference numbers on coins with ink or paint was the standard operating procedure in many museums for the last few centuries before the latter part of the 21st. It's interesting that this has a museum number on it - it must have been part of a museum collection at some point. It is far less worn than most Roman coins found on the Indian sub-continent or eastern Asia. I'd make a guess (but not a bet) that this was lost from a collection (public or private) or de-acquisitioned by a museum within the last century or so.
Folks who peddle in pseudoarchaeology love to use Roman coins found in weird places as evidence for their strange theories, especially coins found in the Americas. https://www.gaia.com/article/out-of-place-artifacts An archaeological podcast for those who like to see fake claims debunked. https://archyfantasies.com/subscribe-to-podcast/ Pieces found in India, Sri Lanka, or Thailand are not so unbelievable.
I live in Arizona, with a lot of ancient ruins around. I alway thought it'd be funny to drop some culls around them. I never would however.
I live in Thailand and I have already dropped a few "culls" at various sites. Let some future archaeologist puzzle over them.