A sample of neon gas at STP is allowed to expand into an evacuated vessel. What is the sign of work for this process?

The sign of work for this process will be Negative.

Explanation:

Work done by the system on the surroundings is negative

So, If work is done on the system, its sign is positive. If work is done by the system, its sign is negative

Here we see the system that is argon gas is expanding and the work is done by the system into the surroundings (vessel) and the sign is Negative

Therefore, the sign of work for this process will be Negative.