Do you acknowledge someone mentioned in your paper/presentation that is in the audience? Say for example you are giving a paper at a conference and someone you name in your paper is in the audience. Is there any expectation that you make reference to this persons presence when giving your presentation?

For example say the text in your paper is;


  Professor X, in his paper on Human mutation...


would you change it to something like;


  Professor X, who is with us today, in his paper on Human mutation...
If you're merely referring to someone's work who you don't know very well or haven't worked with, I wouldn't. If they are someone who is well known then it's likely that people will recognise that they are in the audience and that you are referencing their work.

If it is someone you have worked with or someone in your lab, then they usually get a shoutout. For example, a PI presenting work that is primarily done by a grad student or postdoc is likely to point this out and point out the person if they are in the audience. The reason for this is that it is beneficial to that person to be recognised. It encourages others to talk to/network with them because of the work they've done.