Had a look, it's the Georgia Guidestones - they were commissioned in 1979 by a group of (presumably wealthy) American Christians with some sage advice for humanity:
"A message consisting of a set of ten guidelines or principles is engraved on the Georgia Guidestones in eight different languages, one language on each face of the four large upright stones. Moving clockwise around the structure from due north, these languages are: English, Spanish, Swahili, Hindi, Hebrew, Arabic, Traditional Chinese, and Russian.
Maintain humanity under 500,000,000 in perpetual balance with nature.
Guide reproduction wisely—improving fitness and diversity.
Unite humanity with a living new language.
Rule passion—faith—tradition—and all things with tempered reason.
Protect people and nations with fair laws and just courts.
Let all nations rule internally resolving external disputes in a world court.
Avoid petty laws and useless officials.
Balance personal rights with social duties.
Prize truth—beauty—love—seeking harmony with the infinite.
Be not a cancer on the Earth—Leave room for nature—Leave room for nature."
Seems legit, I'd go for that