The mother in this article said people are telling her... “it’s the Symbol of Mammon — the sign of the Devil’s first born”.
She didn’t say people are telling her... “it’s the Symbol of the Celtic Cross”.
But you are free to keep running interference for Satan... you might want to consider if that is going to work out well for you...
“Some people”
And some people believe crop circles are made by extraterrestrials.
There’s no historical basis for associating that particular symbol with “Mammon”, so whoever is telling them that is merely ignorant. From what I can tell, that particular symbol was made up for the movie “Constantine”. Furhter, any “personification” of Mammon as an actual being is an artifact of later non-religious works such as “The Faerie Queene” by Spenser, or various later occultists. The Bible uses the word exclusively as a metaphor for worldly wealth and money, not for an actual demon.
But hey, you keep adding things to the Bible that aren’t there. I’m sure you know more than its author did.