Officers saw the two men, aged 36 and 49, taking photos of each other making the gesture in front of the Reichstag.
Police said in a statement that the men were questioned at a nearby precinct but later released after leaving a security deposit of 500 euros (USD 593) each.
They face a criminal investigation for using symbols associated with organizations that are considered to be in breach of Germany's constitution. Convictions can incur a fine or a prison sentence of up to three years.