Larry is spot on. :thumbup:
If it has the + it is stainless.
Without the + it could be either one.
If I am buying one for a user, I look for rust spots or little rust pits.
Then I know it is carbon steel, as long as it is not rust transferred onto a ss blade that has been stored next to a rusty carbon blade. I have seen that happen.
One sure way to tell if it is carbon steel is to sharpen it on a belt sander or a super fine stone (not recommended unless you have the proper equipment and a LOT of practice because you sharpen into the oncoming wheel)- If you use either of these methods you will get a shower of sparks with carbon steel. Good stainless does not spark, or gives only an occasional spark.
A word about the grinding wheel-
In the 1980s I went to work in a cutlery store as manager. The sharpening system we had was a Baldor buffer motor (1700 RPM) and a super fine stone. They had come from Gerber knives. It was the system Gerber set up for their dealers at that time to sharpen the Gerber knives, (at least that is what the owner told me). The knives were sharpened into the oncoming wheel.
After sharpening the blade was de-burred on a hard felt wheel with jewelers rouge, but this time it was NOT into the oncoming wheel. One guy tried that, (he forgot), of course it cut into the felt wheel and sent the knife flying into his leg.

Fortunately it did not hit with the edge. It hit him with the handle & bruised his leg. He was very lucky. I finally convinced the owner that we needed a belt sander, which is far more versatile. After we got the belt sander the wheel got very little use.