Just print out a couple of copies of the section on how to tag the monarchs from the website page at http://www.monarchwatch.com/tagmig/tag.htm
~ it clearly indicates (a) how to do it correctly and (b) how this technique is not harmful to the butterflies and more productive scientifically in terms of recovery potential. That, and the website address, should be more than sufficient for those who ask.
Only other thing I can think of that might have people curious is if you're tagging in a public park or other space - some municipalities require permits for that. You could call your local parks & rec offices to check that for your area.