◯ (まる) symbolizes “O.K., Right," Perfect," while X（ばつ）symbolizes "No," "Incorrect," and "Wrong."
The test method that requires the testees to answers in Yes (○) / No (X) format in school examinations and the written examination of driver’s license is called ”まるばつ式テスト.”
I don’t know if ◻ square and △triangle have any specific implications as a sign like ◯ and X have, except the cases of the signs being often used for the index to be placed ahead of the bullet-type sentences, like:
■Fewer people are on welfare
■But the government didn't save money
■Most families in poverty don't receive welfare.