CSM is making all 92Y(supply) sign signature cards for all line companies to pick up supplies from the SSA. Do I have to sign?

Let me see if I understand your question.... your CSM is making all 92Y to sign signature card... fits it all are you the supply clerk for one of the line companies? What kind of unit you are?
I know usually in Aviation by MTOE the line companies didn’t have a 92Y per MTOE, the HHC 92Ys were assigned the line companies as well...

Second if your are deploy are you the only one on the FOB where is a SSA, are the line companies 92Ys have access to the same SSA as well

Lastly have you talk to your S4, if you have questions on something that the CSM is tasking to do well the S4 should be able to explain better what’s going on?

Due to holidays it isn't odd to have signature cards made up to cover for each company if that is your CSMs goal, but he shouldn't even be in the conversation when it comes to signature cards and SSA. We were told SSA had to be cleared during Block leave and if you the supply couldn't pick up then put someone that could on the signature card. Only thing I see wrong in your situation is allowing someone not in your company to sign for you parts. If they want more people on signature to be sure SSA is cleared then they should pull from within their own company.

Note** If you do have to do something to this nature your Commander must agree to allow them on his signature card, if allowed ensure the 1687 has a short term expiration date.

I can understand your hesitation at doing such a thing I was always against that kind of stuff. Step one get with your S4 find out what the true reasoning behind this is. Step two talk with you Commander ( supply works for the Commander not anyone else, including CSM) voice your concerns and ask how they want you to deal with it. Three when deployed you want to network as much as possible a lot of deployed supply is about who you know and what they have that can help you. What are your real concerns I know what mine would be but if you can’t tactfully voice then to your Commander to make them understand they can’t help you fight.