I asked my son who is a tech genius about how I could tag trees for agritourism so that visitors could have a self guided experience using a cell phone. He quickly found that RFID tags are available for the purpose. When in proximity the phone powers up the tag giving you a website link to information.
I'm just now exploring the idea so haven't narrowed my sourcing and details etc but often see interest in tree tagging here and at this point it seems like this tech is available.