I had only one incident in my 50+ years where an individual showed up with horn in tow in the audience at an out of town gig we played monthly in Pittsburg at a club called as Little E's. I did not want it to be awkward, especially since my band played nearly all original tunes which would make it difficult for anyone to sit in. However, during one of the tunes, the band went off into an extensive improve, I took that opportunity to invited the individual to the take stage to play. It was a creative way to solve what could have been a difficult situation. My band was a bit miffed with me bringing him up, but the tension was relieved by my inviting him up.
At the time, I did not know that individual with the horn, but he would eventually be well know to me (and many others here on TB) as Dr. Mark. As some people here on TB may recall, that relationship went down into an aka Wynton/Miles downward spiral.