At Hugues, who was responsible for building the Surveyor, Sheldon Shallon was in charge of the scientific study program for the lunar field. Jacques Tiziou, a science journalist based in the United States since the beginning of the space program, revealed this anecdote in his book on the Moon, published by Stock - 1970. Here is an excerpt from it.
Under NASA's contract, jokes were out of the question, but Sheldon Shallon was tired of Soviet probes leaving loaded with emblems and medals in the USSR colours. He decided to take action... He bought for 50 cents a small American flag at the corner drugstore and waited for the moment when, alone with the probe, he could slip the flag secretly into one of the tubes of the structure...".
Four months after Luna 9, Surveyor 1 landed smoothly 13 km from the planned point, near the Flamsteed Crater. With his flag!