Look at the freshly sharpened edge bevel. Real pattern-welded Damascus carries its layers through the whole thickness of the steel, so the pattern continues right down onto a newly ground bevel. A surface etch or print stops at the surface, leaving the bevel plain.
Pattern welding forge-welds layers of different steels into one billet, so the layers run through the blade like the grain in plywood. Grind a fresh bevel and you expose the layers again, and the pattern follows.
A chemically etched or printed pattern sits on the outside only. Sharpen through it and the bevel comes up plain, which is an immediate and unambiguous answer.
Real pattern welding is rarely perfectly regular. Genuine billets show slight variation as the layers move under the hammer. A pattern that repeats with mechanical exactness across the whole blade is worth a second look.
Price is a signal too. Forge welding is labor intensive, and a very cheap knife with a dramatic pattern is more likely to be etched.
Even confirmed pattern welding says nothing about performance, because that depends on which steels went into the billet and how the blade was heat treated. See Damascus versus solid steel.
We describe Damascus items as what the manufacturer specifies them to be.