As a knight myself, I would say that unless your visible ink is crude, vulgar, blasphemous, or just in really bad taste, I wouldn’t worry too much about it. Most of the knights I have met are really not that judgmental (at least from a public standpoint) and will probably judge you on the good works you (hopefully) do. People who judge critically solely on externals will do that in any organization; unfortunately, they are everywhere. Joining the Knights is an indication of the desire you have to live out your faith in a more positive way. Don’t worry about the trolls in life.