The phrase "additional sign" is correct and usable in written English.
It can be used when referring to an extra indication or symbol that provides more information or context.
Example: "The additional sign at the entrance clearly stated the rules for visitors."
Alternatives: "extra indication" or "supplementary signal".
An additional sign of his masculinity was a metal garbage can with a large dent caused by his foot, which he proudly displayed at his newsroom desk.
As an additional sign that things were changing in the world, the president got a finger-wagging from one of Mr Wen's hangers-on.
But that open-ended commitment to easy money has already generated disagreement within the Fed, and every additional sign of renewed economic growth puts Fed officials under more pressure to resume tightening monetary policy.
Players thought to have debilitating injuries are uniformly held out of workouts, so the fact that Pettitte worked out at all was an additional sign that he could pitch in the next seven days.
Angry demonstrations erupted after the airstrikes, and in an additional sign of protest, the Pakistani government decided not to attend an international conference on the future of Afghanistan held last week in Bonn, Germany.
Rebel fighters took over two military bases in Syria after heavy fighting Tuesday, an additional sign that the ragtag force may finally be breaking a weeks-long stalemate and making progress in its battle against the government of President Bashar Assad.
Phoenix Sky Harbor is giving out plastic "travelers' totes," and Atlanta is posting additional signs.
He pondered the traditional solutions – traffic lights, speed bumps, additional signs pestering drivers to slow down.
Just days before Sept. 11, there were additional signs of rapid deterioration in the economy.
Mr. Leahy said this was evidence of additional signs of recovery in the industry.
Furniture, running water, bathroom installations, and electricity are additional signs of prosperity.
