Can My Workplace Tell Me I Cannot Sign (asl) At Work? (in, U.s.)

I hope this is employment law and not something else lol. Location: Indiana, U.S.

I got a new job a few months ago. In case a coworker reads this, I will just say its customer facing but I only interact with guests as they come in or leave. We also have a union, but I cannot join for at least another month so I am not protected.

So, Near where I work we have a decent deaf/hoh community. My roommate is an ASL interpreter on the side so I am learning things to use at work first. The big one is what I am to say as someone leaves. I sign the equivalent as I verbally say a version of "y'all take care and come see us again." We are trained to say a version of this. I have only ever had people voice that they appreciate me using ASL, both hoh and hearing. However, some coworkers dislike it. They say it looks likes "gang signs." I ignored that, but now my store manager has tried to tell me not to, I think.

We are a chain, but a local one. My manager did not say I cannot sign, but in the conversation it was discussed in, said that all stores need to be uniform and the other stores do not sign. They did say if I knew they are deaf/hoh that i can sign, but from my experience most people do not divulge that info if not required due to stigmas. What is work, a coworker I have who is not customer facing but works during the day is deaf and really only signs.

My question is: can they punish me for signing? Also, I am not in the union yet, but when I do I am way more protected, should I just stop until I am in? My work outside of this has been praised by most managers, including the store manager and their manager. Both managers even complimented me on being able to sign. I hope this makes sense, I have other issues of having by coworkers going on that I am trying to fix that makes it hard to fully focus on this issue, but this is the one issue I am unsure of.

Edit: I guess I did not stress this enough, but it is not comfort for guests that is an issue, only uniformity with the other locations. Also, I do say out loud what I sign, not just sign. The worst reaction I get is ignoring it, and all managers had stated they have only heard good things (I had a meeting for the other issues above and I asked