This is a topic that comes up regularly here.
Do some research, make some contacts, learn what's worked so far & try to help build on that.
Or come up with a completely new idea that's so incredibly brilliant that we're blown away.
The best advice right now is to STOP.
You wouldn't ask a store if it's OK to wear a cross while shopping, would you? (Freedom of worship.)
Or to shop with friends? (Freedom of association.)
No, it's assumed that the peaceful exercise of civil rights is permitted everywhere.
The stores that try to do otherwise create a fuss, and get bad publicity.
If a store wouldn't be allowed to prohibit religious or political garb, they can't prohibit people from exercising other civil rights.
Don't ask permission to exercise your civil rights.
People might get the idea they can say "no".
And if a store (more likely, an uninformed low-level wage slave) ever tries to tell you you're doing something against company policy, then you get a copy of that policy and the name & phone for the store & area managers before you leave the store.
Most likely, they're remembering something in orientation about employees not being allowed to defend themselves. They're probably also not allowed to discuss politics on the job, either. Doesn't mean customers can't.