I guess my only thought would be something similar to the do not distract badges I have on my dog's vest when she's working. One of the other things we have is a little like, stop sign thing on our leash that says not to interact. You could maybe try something similar?
Here's a link to the stop sign thing we have since I am unsure the best way to describe it:
https://www.etsy.com/listing/5373400...detail=1&frs=1