Personally I wouldn't show that particular horse at this time because if he accidentally gets someone hurt it falls back on you regardless if you have his tail marked. I know when I got into horses I didn't know what the red ribbon means until it was to late and my horse got kicked. Let me tell you I had it out with the horse owner. I had asked and she didn't tell me I was pissed. This was a good friend of mine and she knew I had never seen that before.
Needless to say we don't ride no more. It is better to let people know at the show maybe even have them announce it over the intercom so no one gets hurt.